Wireless communication method and wireless communication terminal

ABSTRACT

Provided is a wireless communication terminal. The wireless communication terminal includes: a transceiver configured for transmitting/receiving a wireless signal; and a processor configured for controlling an operation of the wireless communication terminal. The transceiver receives a first frame indicating that there is data to be transmitted from a base wireless communication terminal to a plurality of wireless communication terminals including the wireless communication terminal and receives data based on the first frame. The base wireless communication terminal is any one wireless communication terminal different from the plurality of wireless communication terminals.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/511,581 filed on Mar. 15, 2017, which is the U.S. National Stage ofInternational Patent Application No. PCT/KR2015/009663 filed on Sep. 15,2015, which claims the priority to Korean Patent Application No.10-2014-0121771 filed in the Korean Intellectual Property Office on Sep.15, 2014, Korean Patent Application No. 10-2014-0137941 filed in theKorean Intellectual Property Office on Oct. 13, 2014, and Korean PatentApplication No. 10-2014-0148481 filed in the Korean IntellectualProperty Office on Oct. 29, 2014, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a wireless communication method and awireless communication terminal for setting a broadband link. Morespecifically, the present invention relates to a wireless communicationmethod and a wireless communication terminal for increasing datacommunication efficiency by expanding a data transmission bandwidth of aterminal.

BACKGROUND ART

In recent years, with supply expansion of mobile apparatuses, a wirelessLAN technology that can provide a rapid wireless Internet service to themobile apparatuses has been significantly spotlighted. The wireless LANtechnology allows mobile apparatuses including a smart phone, a smartpad, a laptop computer, a portable multimedia player, an embeddedapparatus, and the like to wirelessly access the Internet in home or acompany or a specific service providing area based on a wirelesscommunication technology in a short range.

Institute of Electrical and Electronics Engineers (IEEE) 802.11 hascommercialized or developed various technological standards since aninitial wireless LAN technology is supported using frequencies of 2.4GHz. First, the IEEE 802.11b supports a communication speed of a maximumof 11 Mbps while using frequencies of a 2.4 GHz band. IEEE 802.11a whichis commercialized after the IEEE 802.11b uses frequencies of not the 2.4GHz band but a 5 GHz band to reduce an influence by interference ascompared with the frequencies of the 2.4 GHz band which aresignificantly congested and improves the communication speed up to amaximum of 54 Mbps by using an OFDM technology. However, the IEEE802.11a has a disadvantage in that a communication distance is shorterthan the IEEE 802.11b. In addition, IEEE 802.11g uses the frequencies ofthe 2.4 GHz band similarly to the IEEE 802.11b to implement thecommunication speed of a maximum of 54 Mbps and satisfies backwardcompatibility to significantly come into the spotlight and further, issuperior to the IEEE 802.11a in terms of the communication distance.

Moreover, as a technology standard established to overcome a limitationof the communication speed which is pointed out as a weak point in awireless LAN, IEEE 802.11n has been provided. The IEEE 802.11n aims atincreasing the speed and reliability of a network and extending anoperating distance of a wireless network. In more detail, the IEEE802.11n supports a high throughput (HT) in which a data processing speedis a maximum of 540 Mbps or more and further, is based on a multipleinputs and multiple outputs (MIMO) technology in which multiple antennasare used at both sides of a transmitting unit and a receiving unit inorder to minimize a transmission error and optimize a data speed.Further, the standard can use a coding scheme that transmits multiplecopies which overlap with each other in order to increase datareliability.

As the supply of the wireless LAN is activated and further, applicationsusing the wireless LAN are diversified, the need for new wireless LANsystems for supporting a higher throughput (very high throughput (VHT))than the data processing speed supported by the IEEE 802.11n has comeinto the spotlight. Among them, IEEE 802.11ac supports a wide bandwidth(80 to 160 MHz) in the 5 GHz frequencies. The IEEE 802.11ac standard isdefined only in the 5 GHz band, but initial 11ac chipsets will supporteven operations in the 2.4 GHz band for the backward compatibility withthe existing 2.4 GHz band products. Theoretically, according to thestandard, wireless LAN speeds of multiple stations are enabled up to aminimum of 1 Gbps and a maximum single link speed is enabled up to aminimum of 500 Mbps. This is achieved by extending concepts of a radiointerface accepted by 802.11n, such as a wider radio frequency bandwidth(a maximum of 160 MHz), more MIMO spatial streams (a maximum of 8),multi-user MIMO, and high-density modulation (a maximum of 256 QAM).Further, as a scheme that transmits data by using a 60 GHz band insteadof the existing 2.4 GHz/5 GHz, IEEE 802.11ad has been provided. The IEEE802.11ad is a transmission standard that provides a speed of a maximumof 7 Gbps by using a beamforming technology and is suitable for high bitrate moving picture streaming such as massive data or non-compression HDvideo. However, since it is difficult for the 60 GHz frequency band topass through an obstacle, it is disadvantageous in that the 60 GHzfrequency band can be used only among devices in a short-distance space.

Meanwhile, in recent years, as next-generation wireless LAN standardsafter the 802.11ac and 802.11ad, discussion for providing ahigh-efficiency and high-performance wireless LAN communicationtechnology in a high-density environment is continuously performed. Thatis, in a next-generation wireless LAN environment, communication havinghigh frequency efficiency needs to be provided indoors/outdoors underthe presence of high-density stations and access points (APs) andvarious technologies for implementing the communication are required.

Especially, as the number of devices using a wireless LAN increases, itis necessary to efficiently use a predetermined channel. Therefore,required is a technology capable of efficiently using bandwidths bysimultaneously transmitting data between a plurality of stations andAPs.

DISCLOSURE Technical Problem

An object of the present invention is to provide an efficient wirelesscommunication method and wireless communication terminal.

Another object of the present invention is to provide a wirelesscommunication method in which one wireless communication terminaltransmits data to a plurality of wireless communication terminalssimultaneously and a wireless communication terminal.

Another object of the present invention is to provide a wirelesscommunication method in which a plurality of wireless communicationterminals transmit data to one wireless communication terminalsimultaneously and a wireless communication terminal.

Technical Solution

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, there isprovided a wireless communication terminal including: a transceiver fortransmitting/receiving a wireless signal; and a processor forcontrolling an operation of the wireless communication terminal, whereinthe transceiver receives a first frame indicating that there is data tobe transmitted from a base wireless communication terminal to aplurality of wireless communication terminals including the wirelesscommunication terminal and receives data based on the first frame,wherein the base wireless communication terminal is any one wirelesscommunication terminal different from the plurality of wirelesscommunication terminals.

The first frame may include a plurality of identifiers for respectivelyidentifying the plurality of wireless communication terminals.

The transceiver may transmit to the base wireless communication terminala second frame indicating that the wireless communication terminal isready to receive data based on the first frame.

The transceiver may receive data from the base wireless communicationterminal and receive information indicating that data transmission isterminated.

The processor may enter a sleep mode based on the information that thedata transmission is terminated.

The information that the data transmission is terminated may include arepeating specific pattern.

The processor may maintain the sleep mode until data transmission forthe plurality of wireless communication terminals of the base wirelesscommunication terminal is completed and wake up when the datatransmission for the plurality of wireless communication terminals ofthe base wireless communication terminal is completed.

The transceiver may receive information indicating that the transmissionis terminated and transmit a third frame indicating whether data isreceived to any one wireless communication terminal among the pluralityof wireless communication terminals, and any one wireless communicationterminal among the plurality of wireless communication terminals may bea wireless communication terminal different from the wirelesscommunication terminal.

Any one wireless communication terminal among the plurality of wirelesscommunication terminals may transmit to the base wireless communicationterminal a fourth frame indicating whether any one wirelesscommunication terminal among the plurality of wireless communicationterminals receives data and whether the wireless communication terminalreceives data based on the third frame.

The transceiver may receive a fifth frame indicating a method ofaccessing the base wireless communication terminal.

The fifth frame may include at least one of an access time point foraccessing the base wireless communication terminal, an orthogonal codeused for access, and a channel used for access.

The fifth frame may include information on a plurality of channelsaccessible to the base wireless communication terminal, wherein theprocessor may access the base wireless communication terminal byselecting any one of the plurality of channels.

The fifth frame may be identical to the first frame.

The plurality of wireless communication terminals may communicate withthe base wireless communication terminal through one Radio Frequency(RF)-chain.

The plurality of wireless communication terminal may have a timedifference between times required for receiving data from the basewireless communication terminal within a reference value.

According to another aspect of the present invention, there is provideda base wireless communication terminal including: a transceiver fortransmitting/receiving a wireless signal; and a processor configured forcontrolling an operation of the wireless communication terminal, whereinthe transceiver transmits a first frame indicating that there is data tobe transmitted from the base wireless communication terminal to aplurality of wireless communication terminals and transmits data to theplurality of wireless communication terminals, wherein the base wirelesscommunication terminal is any one wireless communication terminaldifferent from the plurality of wireless communication terminals.

The first frame may include a plurality of identifiers for respectivelyidentifying the plurality of wireless communication terminals.

The transceiver may receive a second frame indicating ready to receivedata from the plurality of wireless communication terminals, andtransmit data to the plurality of wireless communication terminals basedon the second frame.

The transceiver may complete data transmission to any one wirelesscommunication terminal among the plurality of wireless communicationterminals while transmitting data to the plurality of wirelesscommunication terminals, and transmit information indicating that datatransmission is completed to any one wireless communication terminalamong the plurality of wireless communication terminals.

According to a further another aspect of the present invention, there isprovided an operation method of a wireless communication terminal, themethod including: receiving a first frame indicating there is data to betransmitted from a base wireless communication terminal to a pluralityof wireless communication terminals including the wireless communicationterminal; and receiving data based on the first frame, wherein the basewireless communication terminal is any one wireless communicationterminal different from the plurality of wireless communicationterminals.

Advantageous Effects

One embodiment of the present invention provides an efficient wirelesscommunication method and wireless communication terminal.

Especially, one embodiment of the present invention provides a wirelesscommunication method in which one wireless communication terminaltransmits data to a plurality of wireless communication terminalssimultaneously and a wireless communication terminal.

In addition, one embodiment of the present invention provides a wirelesscommunication method in which a plurality of wireless communicationterminals transmit data to one wireless communication terminalsimultaneously and a wireless communication terminal.

DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a wireless LAN system according to anembodiment of the present invention.

FIG. 2 is a view illustrating a wireless LAN system according to anotherembodiment of the present invention.

FIG. 3 is a block diagram illustrating a configuration of a stationaccording to an embodiment of the present invention.

FIG. 4 is a block diagram illustrating a configuration of an accesspoint according to an embodiment of the present invention.

FIG. 5 is a view illustrating a process that a station sets an accesspoint and a link according to an embodiment of the present invention.

FIG. 6 is a view illustrating that an access point transmits data to aplurality of stations according to an embodiment of the presentinvention.

FIG. 7 is a view illustrating that an access point transmits data toeach of a plurality of stations by independently using each of aplurality of RF-chains according to another embodiment of the presentinvention.

FIG. 8 is a view illustrating that an access point groups a plurality ofstations into a plurality of groups and transmits data by independentlyallocating a plurality of RF-chains to the respective groups accordingto another embodiment of the present invention.

FIG. 9 is a view illustrating that an access point transmits data to aplurality of stations through different access methods for each of aplurality of RF-chains according to another embodiment of the presentinvention.

FIG. 10 is a view illustrating that, when an access point transmits datato a plurality of stations, a station that receives data first among theplurality of stations performs micro-sleep according to an embodiment ofthe present invention.

FIG. 11 is a view illustrating that, when an access point transmits datato a plurality of stations, data is transmitted to another station byusing a channel allocated to a station that receives data first amongthe plurality of stations according to an embodiment of the presentinvention.

FIG. 12 is a view illustrating the format of a frame indicating achannel allocated to a wireless communication terminal according to anembodiment of the present invention.

FIG. 13 is a view illustrating that when transmitting data to aplurality of stations, an access point receives a frame indicatingwhether data of the plurality of stations is received according to anembodiment of the present invention.

FIG. 14 is a view illustrating that a plurality of stations generate aframe indicating whether the plurality of stations receive data receivedata according to an embodiment of the present invention.

FIG. 15 is a view illustrating the format of a frame indicating whethera plurality of wireless communication terminals receive data accordingto an embodiment of the present invention.

FIG. 16 is a view illustrating that a plurality of stations transmitdata to an access point according to an embodiment of the presentinvention.

FIG. 17 is a view illustrating that a plurality of stations transmitdata while reducing the processing burden of an access point accordingto an embodiment of the present invention.

FIG. 18 is a view illustrating a basic service set including a pluralityof stations and an access point according to an embodiment of thepresent invention.

FIG. 19 is a view illustrating that an access point transmits data to aplurality of stations by using a frame indicating that data istransmitted to a plurality of wireless communication terminals accordingto an embodiment of the present invention.

FIG. 20 is a view illustrating the format of a frame indicating achannel to be used to access a first wireless communication terminal bya second wireless communication terminal according to an embodiment ofthe present invention.

FIG. 21 is a view illustrating a structure of an extension field of aframe indicating that there is data to be transmitted to a plurality ofsecond wireless communication terminals according to an embodiment ofthe present invention.

FIG. 22 is a view illustrating that an access point transmits data to aplurality of stations by using a frame indicating that data istransmitted to a plurality of wireless communication terminals accordingto another embodiment of the present invention.

FIG. 23 is a ladder diagram illustrating an operation that a firstwireless communication terminal transmits data to a second wirelesscommunication terminal according to an embodiment of the presentinvention.

FIG. 24 is a ladder diagram illustrating a frame transmission operationof a wireless communication terminal according to an embodiment of thepresent invention.

MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings. The presentinvention may, however, be embodied in different forms and should not beconstructed as limited to the embodiments set forth herein. Parts notrelating to description are omitted in the drawings in order to clearlydescribe the present invention and like reference numerals refer to likeelements throughout.

Furthermore, when it is described that one comprises (or includes orhas) some elements, it should be understood that it may comprise (orinclude or has) only those elements, or it may comprise (or include orhave) other elements as well as those elements if there is no specificlimitation.

This application claims priority to and the benefit of Korean PatentApplication Nos. 10-2014-01217, Nos. 10-2014-0137941, and Nos10-2014-0148481 filed in the Korean Intellectual Property Office and theembodiments and mentioned items described in the respective applicationsare included in the Detailed Description of the present application.

FIG. 1 is a diagram illustrating a wireless LAN system according to anembodiment of the present invention. The wireless LAN system includesone or more basic service sets (BSS) and the BSS represents a set ofapparatuses which are successfully synchronized with each other tocommunicate with each other. In general, the BSS may be classified intoan infrastructure BSS and an independent BSS (IBSS) and FIG. 1illustrates the infrastructure BSS between them.

As illustrated in FIG. 1, the infrastructure BSS (BSS1 and BSS2)includes one or more stations STA1, STA2, STA3, STA4, and STA5, accesspoints PCP/AP-1 and PCP/AP-2 which are stations providing a distributionservice, and a distribution system (DS) connecting the multiple accesspoints PCP/AP-1 and PCP/AP-2.

The station (STA) is a predetermined device including medium accesscontrol (MAC) following a regulation of an IEEE 802.11 standard and aphysical layer interface for a radio medium, and includes both anon-access point (non-AP) station and an access point (AP) in a broadsense. Further, in the present specification, a term ‘terminal’ may beused to refer to a concept including a wireless LAN communication devicesuch as non-AP STA, or an AP, or both terms. A station for wirelesscommunication includes a processor and a transceiver and according tothe embodiment, may further include a user interface unit and a displayunit. The processor may generate a frame to be transmitted through awireless network or process a frame received through the wirelessnetwork and besides, perform various processing for controlling thestation. In addition, the transceiver is functionally connected with theprocessor and transmits and receives frames through the wireless networkfor the station.

The access point (AP) is an entity that provides access to thedistribution system (DS) via wireless medium for the station associatedtherewith. In the infrastructure BSS, communication among non-APstations is, in principle, performed via the AP, but when a direct linkis configured, direct communication is enabled even among the non-APstations. Meanwhile, in the present invention, the AP is used as aconcept including a personal BSS coordination point (PCP) and mayinclude concepts including a centralized controller, a base station(BS), a node-B, a base transceiver system (BTS), and a site controllerin a broad sense.

A plurality of infrastructure BSSs may be connected with each otherthrough the distribution system (DS). In this case, a plurality of BSSsconnected through the distribution system is referred to as an extendedservice set (ESS).

FIG. 2 illustrates an independent BSS which is a wireless LAN systemaccording to another embodiment of the present invention. In theembodiment of FIG. 2, duplicative description of parts, which are thesame as or correspond to the embodiment of FIG. 1, will be omitted.

Since a BSS3 illustrated in FIG. 2 is the independent BSS and does notinclude the AP, all stations STA6 and STA7 are not connected with theAP. The independent BSS is not permitted to access the distributionsystem and forms a self-contained network. In the independent BSS, therespective stations STA6 and STA7 may be directly connected with eachother.

FIG. 3 is a block diagram illustrating a configuration of a station 100according to an embodiment of the present invention.

As illustrated in FIG. 3, the station 100 according to the embodiment ofthe present invention may include a processor 110, a transceiver 120, auser interface unit 140, a display unit 150, and a memory 160.

First, the transceiver 120 transmits and receives a radio signal such asa wireless LAN packet, or the like and may be embedded in the station100 or provided as an exterior. According to the embodiment, thetransceiver 120 may include at least one transmit/receive module usingdifferent frequency bands. For example, the transceiver 120 may includetransmit/receive modules having different frequency bands such as 2.4GHz, 5 GHz, and 60 GHz. According to an embodiment, the station 100 mayinclude a transmit/receive module using a frequency band of 6 GHz ormore and a transmit/receive module using a frequency band of 6 GHz orless. The respective transmit/receive modules may perform wirelesscommunication with the AP or an external station according to a wirelessLAN standard of a frequency band supported by the correspondingtransmit/receive module. The transceiver 120 may operate only onetransmit/receive module at a time or simultaneously operate multipletransmit/receive modules together according to the performance andrequirements of the station 100. When the station 100 includes aplurality of transmit/receive modules, each transmit/receive module maybe implemented by independent elements or a plurality of modules may beintegrated into one chip.

Next, the user interface unit 140 includes various types of input/outputmeans provided in the station 100. That is, the user interface unit 140may receive a user input by using various input means and the processor110 may control the station 100 based on the received user input.Further, the user interface unit 140 may perform output based on acommand of the processor 110 by using various output means.

Next, the display unit 150 outputs an image on a display screen. Thedisplay unit 150 may output various display objects such as contentsexecuted by the processor 110 or a user interface based on a controlcommand of the processor 110, and the like. Further, the memory 160stores a control program used in the station 100 and various resultingdata. The control program may include an access program required for thestation 100 to access the AP or the external station.

The processor 110 of the present invention may execute various commandsor programs and process data in the station 100. Further, the processor110 may control the respective units of the station 100 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 110 may execute the program foraccessing the AP stored in the memory 160 and receive a communicationconfiguration message transmitted by the AP. Further, the processor 110may read information on a priority condition of the station 100 includedin the communication configuration message and request the access to theAP based on the information on the priority condition of the station100. The processor 110 of the present invention may represent a maincontrol unit of the station 100 and according to the embodiment, theprocessor 110 may represent a control unit for individually controllingsome component of the station 100, for example, the transceiver 120, andthe like. The processor 110 controls various operations of radio signaltransmission/reception of the station 100 according to the embodiment ofthe present invention. A detailed embodiment thereof will be describedbelow.

The station 100 illustrated in FIG. 3 is a block diagram according to anembodiment of the present invention, where separate blocks areillustrated as logically distinguished elements of the device.Accordingly, the elements of the device may be mounted in a single chipor multiple chips depending on design of the device. For example, theprocessor 110 and the transceiver 120 may be implemented while beingintegrated into a single chip or implemented as a separate chip.Further, in the embodiment of the present invention, some components ofthe station 100, for example, the user interface unit 140 and thedisplay unit 150 may be optionally provided in the station 100.

FIG. 4 is a block diagram illustrating a configuration of an AP 200according to an embodiment of the present invention.

As illustrated in FIG. 4, the AP 200 according to the embodiment of thepresent invention may include a processor 210, a transceiver 220, and amemory 260. In FIG. 4, among the components of the AP 200, duplicativedescription of parts which are the same as or correspond to thecomponents of the station 100 of FIG. 2 will be omitted.

Referring to FIG. 4, the AP 200 according to the present inventionincludes the transceiver 220 for operating the BSS in at least onefrequency band. As described in the embodiment of FIG. 3, thetransceiver 220 of the AP 200 may also include a plurality oftransmit/receive modules using different frequency bands. That is, theAP 200 according to the embodiment of the present invention may includetwo or more transmit/receive modules among different frequency bands,for example, 2.4 GHz, 5 GHz, and 60 GHz together. Preferably, the AP 200may include a transmit/receive module using a frequency band of 6 GHz ormore and a transmit/receive module using a frequency band of 6 GHz orless. The respective transmit/receive modules may perform wirelesscommunication with the station according to a wireless LAN standard of afrequency band supported by the corresponding transmit/receive module.The transceiver 220 may operate only one transmit/receive module at atime or simultaneously operate multiple transmit/receive modulestogether according to the performance and requirements of the AP 200.

Next, the memory 260 stores a control program used in the AP 200 andvarious resulting data. The control program may include an accessprogram for managing the access of the station. Further, the processor210 may control the respective units of the AP 200 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 210 may execute the program foraccessing the station stored in the memory 260 and transmitcommunication configuration messages for one or more stations. In thiscase, the communication configuration messages may include informationabout access priority conditions of the respective stations. Further,the processor 210 performs an access configuration according to anaccess request of the station. The processor 210 controls variousoperations such as radio signal transmission/reception of the AP 200according to the embodiment of the present invention. A detailedembodiment thereof will be described below.

FIG. 5 is a diagram schematically illustrating a process in which a STAsets a link with an AP.

Referring to FIG. 5, the link between the STA 100 and the AP 200 is setthrough three steps of scanning, authentication, and association in abroad way. First, the scanning step is a step in which the STA 100obtains access information of BSS operated by the AP 200. A method forperforming the scanning includes a passive scanning method in which theAP 200 obtains information by using a beacon message (S101) which isperiodically transmitted and an active scanning method in which the STA100 transmits a probe request to the AP (S103) and obtains accessinformation by receiving a probe response from the AP (S105).

The STA 100 that successfully receives wireless access information inthe scanning step performs the authentication step by transmitting anauthentication request (S107 a) and receiving an authentication responsefrom the AP 200 (S107 b). After the authentication step is performed,the STA 100 performs the association step by transmitting an associationrequest (S109 a) and receiving an association response from the AP 200(S109 b).

Meanwhile, an 802.1X based authentication step (S111) and an IP addressobtaining step (S113) through DHCP may be additionally performed. InFIG. 5, the authentication server 300 is a server that processes 802.1Xbased authentication with the STA 100 and may be present in physicalassociation with the AP 200 or present as a separate server.

When data is transmitted using Orthogonal Frequency Division Modulationor Multi Input Multi Output (MIMO), any one wireless communicationterminal may transmit data to a plurality of wireless communicationterminals simultaneously. Also, any one wireless communication terminalmay simultaneously receive data from a plurality of wirelesscommunication terminals. An embodiment of the present invention will bedescribed through FIGS. 6 to 24, in which any one wireless communicationterminal transmits data to a plurality of wireless communicationterminals and a plurality of wireless communication terminals transmitdata to any one wireless communication terminal. Especially, anembodiment of the present invention will be described in which awireless communication terminal prevents other wireless communicationterminals from accessing a channel and synchronizes data transmission.

For convenience of description, any one wireless communication terminalthat communicates simultaneously with a plurality of wirelesscommunication terminals is referred to as a first wireless communicationterminal and a plurality of wireless communication terminals thatsimultaneously communicate with the first wireless communicationterminal are referred to as a plurality of second wireless communicationterminals. In addition, the first wireless communication terminal may bereferred to as a base wireless communication terminal. In addition, thefirst wireless communication terminal may be a wireless communicationterminal that allocates a communication medium resource and performsscheduling in communication with a plurality of wireless communicationterminals. Specifically, the first wireless communication terminal mayperform the role of a cell coordinator. At this time, the first wirelesscommunication terminal may be the access point 200. In addition, thesecond wireless communication terminal may be the station 100 associatedwith the access point 200. In a specific embodiment, the first wirelesscommunication terminal may be a wireless communication terminal thatallocates a communication medium resource and performs scheduling in anindependent network, such as an ad-hoc network, which is not connectedto an external distribution service. In addition, the first wirelesscommunication terminal may be at least one of a base station, an eNB,and a transmission point TP.

FIG. 6 is a view illustrating that an access point transmits data to aplurality of stations according to an embodiment of the presentinvention.

As described above, the first wireless communication terminal maytransmit data to the plurality of second wireless communicationterminals. At this time, the first wireless communication terminal maytransmit data to each of the plurality of second wireless communicationterminals through a channel allocated to each of the plurality of secondwireless communication terminals. In addition, the first wirelesscommunication terminal may transmit data to each of the plurality ofsecond wireless communication terminals through a channel allocated toeach of the plurality of second wireless communication terminals byusing one radio frequency (RF)-chain. At this time, the sizes of datathat the first wireless communication terminal transmits to theplurality of second wireless communication terminals may be alldifferent. In such a case, the first wireless communication terminal maynot change data transmission for any one second wireless communicationterminal into a reception state until data transmission for all theplurality of second wireless communication terminals is completed.Therefore, the duration field value of a frame indicating that there isdata transmitted from the first wireless communication terminal to theplurality of second wireless communication terminals may be a valuebased on data having the longest transmission time among data to betransmitted to each of the plurality of second wireless communicationterminals. At this time, the duration field indicates a value used forsetting a Network Allocation Vector (NAV).

When the data transmission of the first wireless communication terminalwith respect to any one second wireless communication terminal among theplurality of second wireless communication terminals is completed,another wireless communication terminal not participating in thetransmission may access a corresponding channel. In order to preventthis, the first wireless communication terminal may transmit dummy datato any one second wireless communication terminal that have completedtransmission before data transmission for the plurality of secondwireless communication terminals is all completed. At this time, thedummy data represents meaningless data that is distinguished frommeaningful data transmitted through a data frame. Specifically, thedummy data may be a continuous pattern of a specific value such as “0”.Specifically, the first wireless communication terminal may transmitdata to the second wireless communication terminal after thetransmission of a data frame. At this point, the data frame is a framefor transmitting data distinguished from a control frame. Specifically,the first wireless communication terminal may transmit dummy data aftertransmitting the FCS field of a data frame to the second wirelesscommunication terminal. At this time, the second wireless communicationterminal may ignore the dummy data. In a specific embodiment, the dummydata may be referred to as a busytone.

In another specific embodiment, the first wireless communicationterminal may repeatedly transmit data to any one second wirelesscommunication terminal that completes transmission before datatransmissions for the plurality of second wireless communicationterminals are all completed. At this point, the first wirelesscommunication terminal may again transmit the same data frame to thesecond wireless communication terminal after the transmission of a dataframe. Specifically, the first wireless communication terminal maytransmit the same data frame again after transmitting the FCS field of adata frame to the second wireless communication terminal. At this time,the second wireless communication terminal may ignore the repeatedlytransmitted data.

In the embodiment of FIG. 6, the access point AP transmits a Request ToSend (RTS) frame indicating that there is data to be transmitted to thefirst station STA1, the second station STA2, the third station STA3, andthe fourth station STA4 (S601). At this point, specifically, the accesspoint AP transmits the RTS frame to the first station STA1 through aprimary channel Primary. Also, the access point AP transmits the RTSframe to the fourth station STA4 through the first secondary channelSecondary 1. Additionally, the access point AP transmits the RTS frameto the second station STA2 through the second secondary channelSecondary 2. In addition, the access point AP transmits the RTS frame tothe third station STA3 through the third secondary channel Secondary 3.

The first station STA1, the second station STA2, the third station STA3,and the fourth station STA4 transmit a Clear To Send (CTS) frameindicating ready to receive to the access point AP (S602). At this time,the duration field value of the CTS frame is based on the datatransmission time for the first station STA1, which takes the largesttransmission time.

The access point AP transmits data to the first station STA1, the secondstation STA2, the third station STA3, and the fourth station STA4(S603). Specifically, the access point AP transmits data to the firststation STA1 through a primary channel Primary. Additionally, the accesspoint AP transmits data to the fourth station STA4 through the firstsecondary channel Secondary 1. Additionally, the access point APtransmits data to the second station STA2 through the second secondarychannel Secondary 2. Additionally, the access point AP transmits data tothe third station STA3 through the third secondary channel Secondary 3.

At this time, before completing transmission for the first station STA1,the access point AP completes data transmission for the second stationSTA2, the third station STA3, and the fourth station STA4. At this time,the access point AP transmits dummy data to the second station STA2, thethird station STA3, and the fourth station, or transmits the previouslytransmitted data again.

The first station STA1, the second station STA2, the third station STA3,and the fourth station STA4 transmit an Acknowledgement (ACK) frameindicating whether data is received to the access point AP (S604).Specifically, after the data transmission of the access point AP for thefirst station STA1 is completed and then a predetermined time elapses,the first station STA1, the second station STA2, the third station STA3,and the fourth station STA4 transmit an ACK frame to the access pointAP. At this time, the predetermined time may be a Short Inter-FrameSpace (SIFS) defined in 802.11.

In the case of the above-described embodiment, the first wirelesscommunication terminal may not receive data from the second wirelesscommunication terminal or perform communication with another datacommunication terminal until data transmissions for all the secondwireless communication terminals are completed. Accordingly, theprocessing ability and the currently usable frequency bandwidth of thefirst wireless communication terminal are wasted. This problem may besolved if the first wireless communication terminal independently useseach of plurality of RF-chains. This will be described with reference toFIGS. 7 to 9.

FIG. 7 is a view illustrating that an access point transmits data toeach of a plurality of stations by independently using each of aplurality of RF-chains according to another embodiment of the presentinvention.

When using a plurality of RF-chains, a first wireless communicationterminal may perform transmission and reception operations independentlyin a plurality of RF-chains. Accordingly, when the first wirelesscommunication terminal allocates a plurality of RF-chains to a pluralityof second wireless communication terminals, respectively, and performscommunication, the first wireless communication terminal may receive aframe indicating whether data is received from the second wirelesscommunication terminal whose data transmission is completed earlier thananother second wireless communication terminal before transmission forthe other second wireless communication terminal is completed.Therefore, it is possible to reduce the calculation burden of the firstwireless communication terminal and maximize the frequency bandutilization efficiency.

In the embodiment of FIG. 7, the access point AP uses four RF-chainsthat respectively use the primary channel Primary, the first secondarychannel Secondary 1, the second secondary channel Secondary 2, and thethird secondary channel Secondary 3. At this time, the access point APallocates the four RF-chains to the first station STA1, the secondstation STA2, the third station STA3, and the fourth station STA4,respectively.

The access point AP transmits data to each of the first station STA1,the second station STA2, the third station STA3, and the fourth stationSTA4 independently. Specifically, after transmitting data to the secondstation STA2, the access point AP receives an ACK frame from the secondstation STA2 before data transmission for the first station STA1, thethird station STA3, and the fourth station STA4 is completed. Then,after transmitting data to the third station STA3, the access point APreceives an ACK frame from the third station STA3 before datatransmission for the first station STA1 and the fourth station STA4 iscompleted. Then, after transmitting data to the fourth station STA4, theaccess point AP receives an ACK frame from the third station STA3 beforedata transmission for the first station STA1 is completed. Then, aftertransmitting data to the first station STA1, the access point APreceives an ACK frame from the first station STA1.

Through such an operation, the first wireless communication terminal mayreturn the used frequency band immediately.

In order to operate a plurality of RF-chains, a plurality of antennasshould be used. Therefore, when the number of usable antennas islimited, the number of RF-chains that are able to be used by the firstwireless communication terminal is limited. In addition, the number ofchannels that one first wireless communication terminal is able tosimultaneously use may be limited. For example, according to the 802.11AC standard, in a frequency band of 160 MHz, the first wirelesscommunication terminal may use eight channels with a bandwidth of 20MHz. In such a case, the first wireless communication terminal may useup to eight RF-chains. Therefore, a method for efficiently using thelimited RF-chain is needed. This will be described with reference toFIG. 8.

FIG. 8 is a view illustrating that an access point groups a plurality ofstations into a plurality of groups and transmits data by independentlyallocating a plurality of RF-chains to the respective groups accordingto another embodiment of the present invention.

In order to efficiently use the limited RF-chain, the first wirelesscommunication terminal may group a plurality of second wirelesscommunication terminals into a plurality of groups, and allocate oneRF-chain to one group including the plurality of second wirelesscommunication terminals. At this time, the first wireless communicationterminal may group the second wireless communication terminals based ona data transmission time required for each of the plurality of secondwireless communication terminals. Specifically, the first wirelesscommunication terminal may determine the plurality of second wirelesscommunication terminals as one group when the time difference of a timerequired for transmitting data to each of the plurality of secondwireless communication terminals is within a reference value. Forexample, the transmission time of data to be transmitted from the firstwireless communication terminal to the first station, which is one ofthe second wireless communication terminals, is 20 ms, and thetransmission time of data to be transmitted to the second station is 21ms. At this time, a reference time value as a reference of grouping is 2ms. In such a case, the first wireless communication terminal maydetermine the first station and the second station as one group. Then,the first wireless communication terminal may transmit data to the firststation and the second station by allocating one RF-chain to the firststation and the second station.

In another specific embodiment, the first wireless communicationterminal may group the plurality of second wireless communicationterminals based on the size of data to be transmitted to each of theplurality of second wireless communication terminals. Specifically, thefirst wireless communication terminal may determine the plurality ofsecond wireless communication terminals as one group when the sizedifference of data to be transmitted to each of the plurality of secondwireless communication terminals is within a reference value. Forexample, the size of data to be transmitted from the first wirelesscommunication terminal to the first station, which is one of the secondwireless communication terminals, is 210 Bytes, and the size of data tobe transmitted to the second station is 220 Bytes. At this time, areference size value as a reference of grouping is 5 Bytes. In such acase, the first wireless communication terminal may determine the firststation and the second station as one group. Then, the first wirelesscommunication terminal may transmit data to the first station and thesecond station by allocating one RF-chain to the first station and thesecond station.

At this time, the first wireless communication terminal may transmitdata to each of the plurality of second wireless communication terminalsbelonging to one group through each of a plurality of channels that arenot adjacent to each other. In such a case, the first wirelesscommunication terminal may nullify a channel between two channels thatare not adjacent to each other. For example, when frequency bands aredivided in the order of a primary channel, a first secondary channel, asecond secondary channel, and a third secondary channel, the firststation and the second station included in the same group may use theprimary channel and the second secondary channel, respectively. At thistime, the first wireless communication terminal may nullify the firstsecondary channel.

In addition, the number of the second wireless communication terminalsincluded in one group may not be limited. Accordingly, the number of thesecond wireless communication terminals included in each of theplurality of groups may be different from each other. For example, thenumber of the second wireless communication terminals included in thefirst group may be two, and the number of the second wirelesscommunication terminals included in the second group may be four.

In the embodiment of FIG. 8, the access point AP groups the firststation STA1, the second station STA2, the third station STA3, and thefourth station STA4 into two groups, and transmits data to each of thetwo groups by using an independent RF-chain.

Specifically, the access point AP determines the first station STA1 andthe fourth station STA4, in which the transmission time (i.e., duration)of data to be transmitted has a difference within a reference value, asthe first group. In addition, the access point AP determines the secondstation STA2 and the third station STA3, in which the transmission time(i.e., duration) of data to be transmitted has a difference within areference value, as the second group. The access point AP allocates oneRF-chain to each of the first group and the second group.

The access point AP transmits data to a station allocated to each groupthrough the allocated RF-chain. Specifically, the access point APtransmits data to the first station STA1 and the fourth station STA4through one RF-chain. At this time, the access point AP first completesthe data transmission for the fourth station STA4 before the datatransmission for the first station STA1. Thereafter, until the datatransmission for the first station STA1 is completed, the access pointAP transmits dummy data or transmits the transmitted data again throughthe first secondary channel Secondary 1 used for the data transmissionfor the fourth station STA4. In addition, the access point AP transmitsdata to the second station STA2 and the third station STA3 through oneRF-chain. At this time, the access point AP first completes the datatransmission for the second station STA2 before the data transmissionfor the third station STA3. Thereafter, until the data transmission forthe third station STA3 is completed, the access point AP may transmitdummy data or transmit the transmitted data again through the thirdsecondary channel Secondary 3 used for the data transmission for thethird station STA3.

Through such an embodiment, the first wireless communication terminalmay efficiently utilize the frequency band and the processing abilitywhile using the limited number of RF-chains.

A wireless communication terminal may periodically occupy a channelaccording to a predetermined period. Such a channel access method may bereferred to as a Point Coordination Function (PCF). In addition, if acorresponding channel is idle for a predetermined time or longer, thewireless communication terminal may use the corresponding channelthrough a contention procedure. Specifically, when a correspondingchannel is idle for a predetermined time or longer, the wirelesscommunication terminal obtains a random value within a predeterminedcontention window value. If a corresponding channel is idle afterwaiting for the obtained random value, the wireless communicationterminal may use the corresponding channel. At this time, thepredetermined time may be a Distributed Inter-Frame Space (DIFS) or anArbitration Inter-Frame Space (AIFS) defined by 802.11. Such a channelaccess method may be referred to as a Distributed Coordination Function(DCF). The wireless communication terminal may selectively use the PCFand the DCF based on the characteristics of the communication trafficbetween the wireless communication terminals. However, when the wirelesscommunication terminal uses DCF and PCF alternately while using oneRF-chain, the wireless connection efficiency may be lowered.

In addition, when independently using a plurality of RF-chains, thewireless communication terminal may access a channel by using the PCFwith respect to any one RF-chain among the plurality of RF-chains, andaccess a channel by using the DCF with respect to another RF-chain. Insuch a case, unlike the case of using one RF-chain, the wirelessconnection efficiency of the wireless communication terminal may beincreased. This will be described with reference to FIG. 9.

FIG. 9 is a view illustrating that an access point transmits data to aplurality of stations through different access methods for each of aplurality of RF-chains according to another embodiment of the presentinvention.

The first wireless communication terminal may transmit data to theplurality of second wireless communication terminals by varying achannel access method of each of the plurality of RF-chains.Specifically, the first wireless communication terminal may occupy achannel according to a predetermined period, with respect to a channelincluded in the first RF-chain among the plurality of RF-chains. Then,with respect to a channel included in the second RF-chain, the firstwireless communication terminal may detect whether a correspondingchannel is idle and occupy a channel through a contention procedure. Ina specific embodiment, in the case of a channel included in the firstRF-chain among the plurality of RF-chains, the first wirelesscommunication terminal may occupy the channel through the PCF and in thecase of a channel included in the second RF-chain, occupy the channelthrough the DCF.

Additionally, the first wireless communication terminal may transmitdata to the plurality of second wireless communication terminals byvarying a channel access method of each of the plurality of RF-chainsbased on the traffic characteristics transmitted through the pluralityof RF-chains. Specifically, the first wireless communication terminalmay transmit data to the plurality of second wireless communicationterminals by varying a channel access method of each of the plurality ofRF-chains according to the traffic class of the second wirelesscommunication terminal connected through the RF-chain. For example, foran RF-chain that connects a second wireless communication terminalhaving a traffic class with a priority that is higher than that of thetraffic class of a second wireless communication terminal connected byanother RF-chain, the first wireless communication terminal may occupythe channel of a corresponding RF-chain through a contention procedure.In addition, for an RF-chain that connects a second wirelesscommunication terminal having a traffic class with a priority that islower than that of the traffic class of a second wireless communicationterminal connected by another RF-chain, the first wireless communicationterminal may occupy the channel of a corresponding RF-chainperiodically.

In the embodiment of FIG. 9, an access point AP communicates with aplurality of stations using two RF-chains. The access point AP occupiesa channel through the DCF with respect to a channel included in thefirst RF-chain. Therefore, the access point AP occupies a channelthrough a contention procedure with respect to a channel included in thefirst RF-chain, and transmits data. In addition, the access point APoccupies a channel through the PCF with respect to a channel included inthe second RF-chain. Therefore, the access point AP occupies a channelaccording to a predetermined period with respect to a channel includedin the second RF-chain, and transmits data. In the embodiment of FIG. 9,the access point AP first occupies a channel included in the secondRF-chain and transmits data. Then, in the order of the first stationSTA1, the third station STA3, the fourth station STA4, and seventhstation STAT occupies a channel included in the second RF-chain andtransmits the data.

Through such an embodiment, the first wireless communication terminalmay increase the efficiency of a channel access and data transmission.

Through FIGS. 7 to 9, an embodiment using a plurality of RF-chainsindependently is described above. Through this, even when the firstwireless communication terminal has a different time required totransmit data to each of the plurality of second wireless communicationterminals, the amount of processing of the first wireless communicationterminal and the second wireless communication terminal may be reduced.In addition, through this, the frequency band may be utilizedefficiently. Through FIGS. 10 to 13, even when the first wirelesscommunication terminal has a different time required to transmit data toeach of the plurality of second wireless communication terminals,another embodiment for reducing the amount of computation of the firstwireless communication terminal and the second wireless communicationterminal and efficiently utilizing a frequency band is described.

FIG. 10 is a view illustrating that, when an access point transmits datato a plurality of stations, a station that receives data first among theplurality of stations performs micro-sleep according to an embodiment ofthe present invention.

The first wireless communication terminal transmits a frame indicating achannel allocated to the second wireless communication terminal to thesecond wireless communication terminal. The duration field value of aframe indicating the channel allocated to the second wirelesscommunication terminal may be a value based on data having the longesttransmission time among data to be transmitted to each of the pluralityof second wireless communication terminals. At this time, the durationfield indicates a value used for setting a Network Allocation Vector(NAV). However, when the first wireless communication terminal transmitsa CTS-to-Self frame to be described later, the duration field value ofthe frame indicating the channel allocated to the second wirelesscommunication terminal may be determined based on a time required fortransmitting data to each second wireless communication terminal thatreceives the frame.

In a specific embodiment, the first wireless communication terminal maytransmit a frame indicating a channel allocated to the second wirelesscommunication terminal through a channel allocated to each of theplurality of second wireless communication terminals. At this time, theframe indicating the channel allocated to the second wirelesscommunication terminal may indicate a time point at which data istransmitted to the second wireless communication terminal. A frameindicating a channel allocated to the second wireless communicationterminal may be referred to as an sRTS frame. The specific format of thesRTS frame will be described later with reference to FIG. 12.

In addition, the channel allocated to the second wireless communicationterminal may be a channel and also a sub-channel that is the sub-band ofthe channel. In such a case, the first wireless communication terminalmay transmit the sRTS frame through the sub-channel allocated to thesecond wireless communication terminal.

Before this, the first wireless communication terminal may transmit aCTS-to-Self frame in which the reception address of a frame indicatingready to receive data is the address of a wireless communicationterminal that transmits a corresponding frame. Specifically, the firstwireless communication terminal may transmit a CTS-to-Self frame througha channel having a sub-channel as a sub-band. Through this, the firstwireless communication terminal does not support the embodiment of thepresent invention, thereby preventing wireless communication terminalsfrom accessing a channel through a sub-channel. Specifically, when thefirst wireless communication terminal transmits a frame indicating achannel allocated to the second wireless communication terminal to thesecond wireless communication terminal through a sub-channel, thewireless communication terminal that monitors only the 20 MHz channelmay not receive the frame. Accordingly, the first wireless communicationterminal may transmit a CTS-to-Self frame before transmitting a frameindicating the channel allocated to the second wireless communicationterminal. Through this, the first wireless communication terminal mayallow a wireless communication terminal that monitors only the 20 MHzchannel to set the NAV. The value of the duration field of theCTS-to-Self frame may be determined based on the longest time requiredto transmit data to each of the plurality of second wirelesscommunication terminals.

The second wireless communication terminal that receives the frameindicating the channel allocated to the second wireless communicationterminal transmits a frame indicating ready to receive data to the firstwireless communication terminal. Specifically, the second wirelesscommunication terminal transmits to the first wireless communicationterminal a frame indicating ready to receive data through the channelallocated to the second wireless communication terminal. At this time,the frame indicating ready to receive data may be a CTS frame.

The first wireless communication terminal transmits data to the secondwireless communication terminal based on the frame indicating ready toreceive the data. At this time, the first wireless communicationterminal may transmit data to the second wireless communication terminaland transmit information indicating that the data transmission iscompleted to the second wireless communication terminal. In such a case,the second wireless communication terminal may enter a sleep mode basedon the information indicating that the data transmission is completed.At this time, the sleep mode indicates that a wireless communicationterminal performs only a certain function in order to reduce powerconsumption. Specifically, the second wireless communication terminalmay enter a sleep mode when receiving the information indicating thatthe data transmission is completed. In addition, the second wirelesscommunication terminal may maintain the sleep mode for a time obtainedby subtracting the elapsed time from the duration field value of theframe indicating the channel allocated to the second wirelesscommunication terminal or the duration field value of the CTS-to-Selfframe.

The information indicating that the transmission is terminated may bepredefined. Additionally, the information indicating that thetransmission is terminated may have a repeated specific pattern.Specifically, the information indicating that the transmission isterminated may be similar to the auto-detection pattern of the preambleof 802.11ac. In a specific embodiment, the information indicating thatthe transmission is terminated may be referred to as an ending-tone.

In another specific embodiment, without the information indicating thatthe transmission is terminated, the second wireless communicationterminal may enter the sleep mode after a lapse of time corresponding tothe duration field value of the frame indicating the channel allocatedto the second wireless communication terminal. In such a case, theduration field value of the frame indicating the channel allocated tothe second wireless communication terminal indicates the time requiredfor transmitting data to be transmitted to the second wirelesscommunication terminal.

In another specific embodiment, the second wireless communicationterminal may enter the sleep mode based on information indicating thenumber of symbols of data included in the preamble of a signal includingdata. Specifically, the second wireless communication terminal mayreceive data as many as the number of symbols indicated by theinformation indicating the number of symbols of data, and enter thesleep mode. At this time, the preambles of all signals transmitted by asub-channel unit may include information indicating the number ofsymbols of data. At this time, the information indicating the number ofsymbols of data included in the preamble of the signal may be referredto as a length field.

When data transmission to all of the plurality of second wirelesscommunication terminals is completed, the second wireless communicationterminal entering the sleep mode may wake-up. Specifically, the secondwireless communication terminal may wake up after a predetermined timeelapses from the time when the second wireless communication terminalenters the sleep mode. At this time, the predetermined time may be atime indicated by the duration field value of a frame indicating achannel allocated to the second wireless communication terminal, or atime obtained by subtracting an elapsed time from the duration fieldvalue of a CTS-to-Self frame.

The plurality of second wireless communication terminals transmit to thefirst wireless communication terminal a frame indicating whether data isreceived or not. Specifically, the plurality of second wirelesscommunication terminals may transmit to the first wireless communicationterminal a frame indicating whether data is received through a channelallocated to each of the plurality of second wireless communicationterminals. At this point, the frame indicating whether data is receivedmay be an ACK frame.

In addition, after receiving a frame indicating whether data is receivedfrom the second wireless communication terminal, the first wirelesscommunication terminal may transmit an ACK-to-Self frame. At this time,the ACK-to-Self frame indicates an ACK frame indicating that thereception address is the first wireless communication terminal thattransmits the ACK-to-Self frame. Specifically, when transmitting datathrough a sub-channel, the first wireless communication terminal maytransmit the ACK-to-Self frame through the channel having acorresponding sub-channel as a sub-band. For example, the first wirelesscommunication terminal may transmit data through a sub-channel having abandwidth of 5 MHz, which is a sub-channel of a channel having abandwidth of 20 MHz, and may receive a frame indicating whether data isreceived through a corresponding sub-channel. At this time, the firstwireless communication terminal may transmit an ACK-to-Self framethrough a channel having a bandwidth of 20 MHz. Through this,compatibility with a wireless communication terminal that does notsupport an embodiment of the present invention and does not monitor asub-channel may be achieved. Also, when the first wireless communicationterminal transmits data through the sub-channel, the duration fieldvalue of a control frame transmitted through a channel unit may be theduration until the ACK-to-Self frame is transmitted. At this time, thecontrol frame may include a CTS-to-Self frame.

In the embodiment of FIG. 10, the access point AP transmits aCTS-to-Self frame through a channel having a bandwidth of 20 MHz(S1001). Through this, the access point AP may allow a station that doesnot support an embodiment of the present invention to set a NAV.

The access point AP transmits a sRTS frame including informationindicating a channel allocated to each of the plurality of stations tothe first station STA1, the second station STA2, and the third stationSTA3 (S1002). Specifically, the access point AP transmits a sRTS frameto the first station STA1, the second station STA2, and the thirdstation STA3 through a channel allocated to each of the first stationSTA1, the second station STA2, STA2, and the third station STA3. At thistime, the channel allocated to each of the first station STA1, thesecond station STA2, and the third station STA3 is a sub-channel of achannel having a bandwidth of 20 MHz. Specifically, the sub-channel mayhave a bandwidth of 5 MHz.

The first station STA1, the second station STA2, and the third stationSTA3 obtain information on a channel allocated to each of the firststation STA1, the second station STA2, the third station STA3, and thefourth station STA4, based on an sRTS frame. Specifically, the firststation STA1 obtains information indicating that a first sub-channelsub-channel 1 and a second sub-channel sub-channel 2 are allocated tothe first station STA1. In addition, the second station STA2 obtainsinformation indicating that a sub-channel 3 is allocated to the secondstation STA2. In addition, the third station STA3 obtains informationindicating that a fourth sub-channel sub-channel 4 is allocated to thesecond station STA2.

The first station STA1, the second station STA2, and the third stationSTA3 transmit a CTS frame indicating ready to receive data through achannel allocated to each of the first station STA1, the second stationSTA2, and the third station STA3 (S1003).

The access point AP receives the CTS frame indicating ready to receivedata.

The access point AP transmits data to each of the first station STA1,the second station STA2, and the third station STA3 based on the CTSframe indicating ready to receive data (S1004). Specifically, the accesspoint AP transmits data to each of the first station STA1, the secondstation STA2, and the third station STA3, which transmit the CTS frame.At this time, the access point AP completes the data transmission forthe second station STA2 and the third station STA3 before the datatransmission for the first station STA1 is completed. The access pointAP transmits an ending tone, which is information indicating that thedata transmission for the second station STA2 and the third station STA3is terminated.

The second station STA2 and the third station STA3 receive data andperform a micro-sleep mode based on an ending tone, which is informationindicating that data transmission is terminated (S1005). The secondstation STA2 and the third station STA3 may wake up based on theduration field value included in the CTS-to-Self frame or the sRTS frameas described above. Specifically, after entering the sleep mode, thesecond station STA2 and the third station STA3 may wake up after a timeobtained by subtracting an elapsed time from a time of receiving aCTS-to-S elf frame to a time of completing data transmission from theduration field value included in the CTS-to-Self. In another specificembodiment, after entering the sleep mode, the second station STA2 andthe third station STA3 may wake up after a time of completing datatransmission from a time of receiving an sRTS frame in the durationfield value included in the sRTS frame.

The first station STA1, the second station STA2, and the third stationSTA3, which receive data, transmit to the access point AP an ACK frameindicating whether data is received through a channel allocated to eachof the first station STA1, the second station STA2, and the thirdstation STA3. At this time, since receiving allocated sub-channels, thefirst station STA1, the second station STA2, and the third station STA3transmit an ACK frame through a sub-channel allocated to each of thefirst station STA1, the second station STA2, and the third station STA3.

The access point AP transmits an ACK-to-Self frame, which is an ACKframe having the reception address of the access point AP, through achannel having a bandwidth of 20 MHz. Through this, the access point APnotifies that the transmission of a wireless communication terminal thatdoes not support an embodiment of the present invention is terminated.

Through such an embodiment, a second wireless communication terminalthat first completes data reception among the plurality of secondwireless communication terminals enters the sleep mode so that it mayreduce the power consumption. However, through such an embodiment, achannel allocated to the second wireless communication terminal is notused while the second wireless communication terminal enters the sleepmode. Therefore, there is a need for a method for utilizing a channelallocated to the second wireless communication terminal when the datatransmission for the second wireless communication terminal is completedand the second wireless communication terminal enters the sleep mode.This will be described with reference to FIG. 11.

FIG. 11 is a view illustrating that, when an access point transmits datato a plurality of stations, data is transmitted to another station byusing a channel allocated to a station that receives data first amongthe plurality of stations according to an embodiment of the presentinvention.

While transmitting data to the plurality of second wirelesscommunication terminals, the first wireless communication terminal mayfirst complete the data transmission for any one of the plurality ofsecond wireless communication terminals. In such a case, the firstwireless communication terminal may transmit data to another secondwireless communication terminal whose data transmission is not completedthrough a channel allocated to any one second wireless communicationterminal whose data transmission is completed. At this time, anothersecond wireless communication terminal may be a second wirelesscommunication terminal whose data transmission is not completed among aplurality of second wireless communication terminals. In anotherspecific embodiment, another second wireless communication terminal maybe a second wireless communication terminal that does not start toreceive data when the data transmission for any one second wirelesscommunication terminal is completed.

In addition, as described above, while transmitting data to theplurality of second wireless communication terminals, the first wirelesscommunication terminal may transmit information indicating that the datatransmission is completed to a second wireless communication terminalwhose data transmission is completed first among the plurality of secondwireless communication terminals. After transmitting the informationindicating that the data transmission is completed, the first wirelesscommunication terminal may transmit data to another second wirelesscommunication terminal through a channel allocated to a second wirelesscommunication terminal whose data transmission is completed first amongthe plurality of second wireless communication terminals.

At this time, the first wireless communication terminal may transmit aguard interval signal before transmitting data after transmitting theinformation indicating that the data transmission is completed in orderto prevent interference between signals. At this time, the guardinterval signal may be a Nulling signal.

As described above, the first wireless communication terminal maytransmit a frame indicating a channel allocated to the second wirelesscommunication terminal. At this time, a frame indicating a channelallocated to the second wireless communication terminal may indicatethat data is transmitted to another second wireless communicationterminal through a channel allocated to a second wireless communicationterminal whose data transmission is completed first among the pluralityof second wireless communication terminals. A structure of a frameindicating a channel allocated to the second wireless communicationterminal for this will be described later with reference to FIG. 12.

In the embodiment of FIG. 11, the access point AP transmits data to thefirst station STA1, the second station STA2, and the third station STA3.At this time, the remaining operations of the access point AP except forthe operation of transmitting data to the first station STA1, the secondstation STA2, and the third station STA3 are the same as those of theembodiment of FIG. 10. Therefore, it will be described that the accesspoint AP transmits data to the first station STA1, the second stationSTA2, and the third station STA3, and a description of other operationswill be omitted.

The access point AP transmits data to each of the first station STA1,the second station STA2, and the third station STA3 based on the CTSframe indicating ready to receive data. Specifically, the access pointAP transmits data to each of the first station STA1, the second stationSTA2, and the third station STA3, which transmit the CTS frame. At thistime, the access point AP completes the data transmission for the secondstation STA2 and the third station STA3 before the data transmission forthe first station STA1 is completed. The access point AP transmits anending tone, which is information indicating that the data transmissionis terminated, to the second station STA2 and the third station STA3. Atthis time, the second station STA2 and the third station STA3 receivedata and perform a micro-sleep mode based on an ending tone, which isinformation indicating that data transmission is terminated (S1101). Thesubsequent operation of the second station STA2 and the third stationSTA3 may be the same as the above-described embodiments.

The access point AP transmits data to the first station STA1 through achannel allocated to the second station STA2 and the third station STA3(S1102). Specifically, the access point AP transmits an ending tone tothe second station STA2 and the third station STA3 through a channelallocated to the second station STA2 and the third station STA3, andtransmits a guard interval signal. After transmitting the guard intervalsignal, the access point AP transmits data to the first station STA1through a channel allocated to the second station STA2 and the thirdstation STA3.

Through this, the first wireless communication terminal may increase theusage efficiency of a frequency band.

FIG. 12 is a view illustrating the format of a frame indicating achannel allocated to a wireless communication terminal according to anembodiment of the present invention.

The frame indicating a channel allocated to the second wirelesscommunication terminal may include information on a channel allocated tothe second wireless communication terminal. At this time, the channelallocated to the second wireless communication terminal may be a channeland also a sub-channel that is the sub-band of the channel.

In addition, the frame indicating the channel allocated to the secondwireless communication terminal may include information on the order inwhich the second wireless communication terminal uses the allocatedchannel. In a specific embodiment, the frame indicating the channelallocated to the second wireless communication terminal may includeinformation that a corresponding second wireless communication terminaluses the allocated channel firstly or secondly. At this time, theinformation on whether the allocated channel is used firstly or secondlyby a corresponding second wireless communication terminal may be in a1-bit flag format. As described above, in a specific embodiment, theframe indicating the channel allocated to the second wirelesscommunication terminal may be referred to as an sRTS frame.

In a specific embodiment as shown in FIG. 12, the sRTS frame may includea Frame Control field indicating information for frame control.

In addition, the sRTS frame may include a Duration field indicatinginformation for NAV setting.

In addition, the sRTS frame may include a Receiver Address fieldindicating information for identifying the second wireless communicationterminal that receives a corresponding frame. At this time, theinformation for identifying the second wireless communication terminalmay be a association identifier for identifying the association of thefirst wireless communication terminal and the second wirelesscommunication terminal. Specifically, the association identifier may bean AID. In another specific embodiment, the information for identifyingthe second wireless communication terminal may be a MAC address.

In addition, the sRTS frame may include a Transmitter Address fieldindicating information for identifying the second wireless communicationterminal that transmits a corresponding frame. At this time, theinformation for identifying the first wireless communication terminalmay indicate the MAC address of a wireless communication terminal.Further, the information for identifying the first wirelesscommunication terminal may be an identifier for identifying a BSSincluded in the first wireless communication terminal.

In addition, the sRTS frame may include a Sub-channel Bitmap fieldindicating a sub-channel allocated to the second wireless communicationterminal. At this time, the Sub-channel Bitmap field may includeinformation indicating whether or not each of the plurality ofsub-channels is allocated and the order in which a corresponding secondwireless communication terminal uses the sub-channel. Specifically, theSub-channel Bitmap field may include a field indicating each of aplurality of sub-channels. In addition, the field indicating eachsub-channel may include a field indicating the order in which the secondwireless communication terminal that receives an allocated correspondingsub-channel uses a corresponding sub-channel. Specifically, the fieldindicating the sub-channel may include a field indicating whether thesecond wireless communication terminal that receives an allocatedcorresponding sub-channel uses a corresponding sub-channel firstly orsecondly. For example, the field representing each of the sub-channelsmay be a 2-bit field. At this time, the first bit of the fieldindicating each of the sub-channels may be a flag bit indicating thatthe second wireless communication terminal that receives an allocatedcorresponding sub-channel uses a corresponding sub-channel firstly. Inaddition, the second bit of the field indicating each of thesub-channels may be a flag bit indicating that the second wirelesscommunication terminal that receives an allocated correspondingsub-channel uses a corresponding sub-channel secondly. In the embodimentof FIG. 12, the first station STA1 uses a first sub-channel sub-channel1 and a second sub-channel sub-channel 2 firstly and uses a thirdsub-channel sub-channel 3 and a fourth sub-channel sub-channel 4secondly. In such a case, the value of the Sub-channel Bitmap field isbinary 10100101. Also, the second station STA2 uses the thirdsub-channel sub-channel 3 firstly. In such a case, the value of theSub-channel Bitmap field is binary 00001000. Also, the third stationSTA3 uses the fourth sub-channel sub-channel 4 firstly. In such a case,the value of the Sub-channel Bitmap field is binary 00000010.

In the case that among the plurality of second wireless communicationterminals, a second wireless communication terminal completestransmission and then immediately transmits a frame indicating whetherdata is received, a corresponding second wireless communication terminalmay continuously maintain the sleep mode without waking up to transmitan ACK frame. However, since the first wireless communication terminalis transmitting data to another second wireless communication terminal,there is a problem that the first wireless communication terminal is notable to receive the frame indicating whether data is received. Anembodiment of the present invention for solving the problem will bedescribed with reference to FIG. 13 to FIG. 15.

FIG. 13 is a view illustrating that when transmitting data to aplurality of stations, an access point receives a frame indicatingwhether data of the plurality of stations is received according to anembodiment of the present invention.

Even if receiving data through a sub-channel, a wireless communicationterminal using a communication method with OFDMA receives a signaltransmitted through an entire band of a channel having a sub-channel asa sub-band. Then, the wireless communication terminal detects datatransmitted through the sub-channel allocated to the wirelesscommunication terminal from the received signal. For example, a wirelesscommunication terminal may receive an allocated sub-channel having a 5MHz bandwidth of a channel having a 20 MHz bandwidth and receive datathrough a corresponding sub-channel. At this time, the wirelesscommunication terminal receives a signal transmitted through the entire20 MHz band. Then, the wireless communication terminal extracts thedata, which is transmitted through the sub-channel allocated to thewireless communication terminal, from the signal of the entire 20 MHzband. Accordingly, the second wireless communication terminal, which isreceiving data from the first wireless communication terminal, mayreceive a frame that another second wireless communication terminaltransmits through a sub-channel not used by the first wirelesscommunication terminal. Therefore, the second wireless communicationterminal that completes data reception firstly among the plurality ofsecond wireless communication terminals may transmit a frame indicatingwhether the second wireless communication terminals receives data toanother second wireless communication terminal. Specifically, the secondwireless communication terminal may transmit a frame indicating whetherthe second wireless communication terminal receives data to anotherwireless communication terminal through a channel allocated to thesecond wireless communication terminal. At this time, another secondwireless communication terminal may be a second wireless communicationterminal that currently receives data. In addition, a frame indicatingwhether data is received or not may be referred to as an sACK.

After all the data transmissions for the plurality of second wirelesscommunication terminals are completed, another second wirelesscommunication terminal transmits a frame indicating whether theplurality of second wireless communication terminals receive data.Specifically, another second wireless communication terminal maytransmit a frame indicating whether the plurality of second wirelesscommunication terminals receive data through a channel having asub-channel allocated to the second wireless communication terminal as asub-band. At this time, a frame indicating whether the plurality ofsecond wireless communication terminals receive data may be referred toas an aggregated (Agg) ACK.

In the embodiment of FIG. 13, the first station STA1, the second stationSTA2, and the third station STA3 transmit a CTS frame indicating readyto receive data through a channel allocated to each of the first stationSTA1, the second station STA2, and the third station STA3. Specifically,the first station STA1 transmits a CTS frame to the access point APthrough each of the first sub-channel sub-channel 1 and the secondsub-channel sub-channel 2. In addition, the second station STA2transmits a CTS frame to the access point AP through the thirdsub-channel sub-channel 3. In addition, the third station STA3 transmitsa CTS frame to the access point AP through the fourth sub-channelsub-channel 4.

The access point AP receives the CTS frame indicating ready to receivedata. The access point AP receives a CTS frame from the first stationSTA1, the second station STA2, and the third station STA3 through achannel allocated to each of the first station STA1, the second stationSTA2, STA2, and the third station STA3.

The access point AP transmits data to each of the first station STA1,the second station STA2, and the third station STA3 based on the CTSframe indicating ready to receive data. Specifically, the access pointAP transmits data to each of the first station STA1, the second stationSTA2, and the third station STA3, which transmit the CTS frame. At thistime, the access point AP completes the data transmission for the secondstation STA2 and the third station STA3 before the data transmission forthe first station STA1 is completed. The access point AP transmits anending tone, which is information indicating that the data transmissionis terminated, to the second station STA2 and the third station STA3.

The second station STA2 and the third station STA3 receive data andtransmit an sACK frame indicating whether data is received based on anending tone, which is information indicating that data transmission isterminated. Specifically, when a predetermined time elapses after thereception of the ending tone, the third station STA3 transmits an sACKframe indicating whether data is received to the second station STA2 orthe first station STA1, each of which is receiving data (S1301). At thistime, the predetermined time may be SIFS defined in 802.11.

In addition, when a predetermined time elapses after the ending tone isreceived by the second station STA2, the second station STA2 transmitsan sACK frame to the first station STA1 that is receiving data (S1302).At this time, when receiving the sACK frame from the first station STA1,the second station STA2 transmits to the first station SAT1 an sACKframe indicating whether the first station STA1 receives data andwhether the second station STA2 receives data.

The second station STA2 and the third station STA3 transmit an sACKframe and perform a micro-sleep mode. Specifically, the second stationSTA2 and the third station STA3 perform a micro-sleep mode after apredetermined time from the transmission of the sACK frame. At thistime, the predetermined time may be XIFS defined in 802.11.

The first station STA1 that completes the data reception transmits anAgg ACK frame indicating whether the first station STA1, the secondstation STA2, and the third station STA3 receive data to the accesspoint AP. At this time, the first station STA1 transmits the Agg ACKframe through a channel having a sub-channel allocated to the firststation STA1 as a sub-band.

A method for generating an Agg ACK, which is a frame indicating whetherthe plurality of second wireless communication terminals receive dataand its specific format will be described with reference to FIGS. 14 and15.

FIG. 14 is a view illustrating that a plurality of stations generate aframe indicating whether the plurality of stations receive data receivedata according to an embodiment of the present invention.

As described above, the second wireless communication terminal thatcompletes data reception among the plurality of second wirelesscommunication terminals may transmit the sACK frame indicating whetherthe second wireless communication terminal receives data to anothersecond wireless communication terminal. At this time, the secondwireless communication terminal should determine whether to transmit thesACK frame to any of the other second wireless communication terminals.The second wireless communication terminal may transmit an sACK frame toanother second wireless communication terminal based on at least any oneof whether another second wireless communication terminal transmits aframe indicating ready to receive data and the duration value of datatransmitted to another second wireless communication terminal.Specifically, the second wireless communication terminal may transmit ansACK frame to another second wireless communication terminal thattransmits a frame indicating ready to receive data. In addition, thesecond wireless communication terminal may transmit an sACK frame toanother second wireless communication terminal that receives data havingthe duration end time point that is later than the time point that thesecond wireless communication terminal transmits the sACK frame. Forexample, the second wireless communication terminal may transmit an sACKframe to any one second wireless communication terminal whose receiveddata duration end time point is later than the time point oftransmitting an sACK frame among a plurality of other second wirelesscommunication terminals that transmit a frame indicating ready toreceive data.

In another specific embodiment, the second wireless communicationterminal may determine another second wireless communication terminalthat is to receive an sACK based on whether another second wirelesscommunication terminal is in a communicable position. Specifically, thesecond wireless communication terminal may transmit an sACK to anothersecond wireless communication terminal that is in a communicableposition. At this time, the second wireless communication terminal mayreceive from the first wireless communication terminal information onwhether the second wireless communication terminal is in a communicableposition.

In the embodiment of FIG. 14(A), the data transmission for the thirdstation STA3 among the first station STA1, the second station STA2, andthe third station STA3 is completed first. The third station STA3generates a third sACK frame indicating whether the third station STA3receives data. The third station STA3 transmits the third sACK frame tothe second station STA2 having the end time point of the data receptionduration later than the transmission time point of the sACK frame.

The second station STA2 generates a second sACK frame based on the thirdsACK frame received from the third station STA3 and whether the secondstation STA2 receives data. The second station STA2 transmits the secondsACK frame to the third station STA3 having the end time point of thedata reception duration later than the transmission time point of thesACK frame.

The first station STA1 generates an Agg ACK frame indicating whether thefirst station STA1, the second station STA2, and the third station STA3receive data based on the second sACK frame and whether the thirdstation STA3 receives data. The third station STA3 transmits the Agg ACKframe to the access point AP.

In the embodiment of FIG. 14(B), the data transmission for the thirdstation STA3 among the first station STA1, the second station STA2, andthe third station STA3 is completed first. The third station STA3transmits the third sACK frame to the first station STA1 having the endtime point of the data reception duration later than the transmissiontime point of the sACK frame.

The second station STA2 generates a second sACK based on whether thesecond station STA2 receives data. The second station STA2 transmits thesecond sACK frame to the first station STA1 having the end time point ofthe data reception duration later than the transmission time point ofthe sACK frame.

The first station STA1 generates an Agg ACK frame indicating whether thefirst station STA1, the second station STA2, and the third station STA3receive data based on the second sACK frame, the third sACK frame, andwhether the first station STA1 receives data. The first station STA1transmits the Agg ACK frame to the access point AP.

FIG. 15 is a view illustrating the format of a frame indicating whethera plurality of wireless communication terminals receive data accordingto an embodiment of the present invention.

The frame indicating whether a plurality of wireless communicationterminals receive data, as described above, may indicate whether theplurality of second wireless communication terminals receive data.

In addition, the frame indicating whether a plurality of wirelesscommunication terminals receive data may include information foridentifying the plurality of wireless communication terminals.Specifically, the information for identifying a plurality of wirelesscommunication terminals may be an identifier for identifying each of theplurality of wireless communication terminals.

In addition, the frame indicating whether a plurality of wirelesscommunication terminals receive data may include information on achannel allocated to each of the plurality of wireless communicationterminals and information indicating whether data transmitted through acorresponding channel is received. Here, the allocated channel mayindicate a channel and also a sub-channel that is the sub-band of thechannel. At this time, the frame indicating whether a plurality ofwireless communication terminals receive data may include information onthe order in which data is transmitted through the allocated channel. Ina specific embodiment, the frame indicating whether a plurality ofwireless communication terminals receive data may include information onwhether the data transmitted through the allocated channel istransmitted firstly or secondly. At this time, the information onwhether data is transmitted firstly or secondly may be in the format ofa 1-bit flag. As described above, in a specific embodiment, the frameindicating whether a plurality of wireless communication terminalsreceive data may be referred to as an Agg ACK frame.

In addition, a structure of such an Agg ACK frame may be equally appliedto the above-described sACK.

In a specific embodiment like FIG. 15, the Agg ACK frame indicatingwhether a plurality of wireless communication terminals receive data mayinclude a Frame Control field including information on frame control.

In addition, the Agg ACK frame may include a Duration field includinginformation for NAV setting.

Also, the Agg ACK frame may include an identifier for identifying awireless communication terminal that receives the Agg ACK frame.

In addition, the Agg ACK frame may include a sub-channel Bitmap fieldindicating information on a sub-channel allocated to each of a pluralityof wireless communication terminals and information indicating whetherdata transmitted through a corresponding sub-channel is received, asdescribed above. The Sub-channel Bitmap field may include information onthe order of data transmitted through a sub-channel. In a specificembodiment, as in the embodiment of FIG. 15, the Sub-channel Bitmapfield includes a field indicating whether the first data transmittedthrough a corresponding sub-channel is transmitted and a fieldindicating whether the second data transmitted through a correspondingsub-channel is transmitted. As in the embodiment of FIG. 15, when thethird station STA3 transmits an Agg ACK frame including a Sub-ChannelBitmap field having a value of 1(00000001b), this indicates that any onestation receives the second data transmitted through the fourthsub-channel. In addition, when the second station transmits an Agg ACKframe including a Sub-Channel Bitmap field having a value of10(00001010b), this indicates that any one station or a plurality ofstations receive the first data transmitted through the thirdsub-channel and the second data transmitted through the fourthsub-channel. In addition, when the first station transmits an Agg ACKframe including a Sub-Channel Bitmap field having a value of175(10101111b), this indicates that any one station or a plurality ofstations receive the first data transmitted through the firstsub-channel, the first data transmitted through the second sub-channel,the first and second data transmitted through the third sub-channel, andthe first and second data transmitted through the fourth sub-channel.

The second wireless communication terminal may continuously maintain thesleep mode through the embodiments described with reference to FIGS. 13to 15.

It is described with reference to FIGS. 6 to 15 that the first wirelesscommunication terminal transmits data to the second wirelesscommunication terminal. In particular, it is described that the firstwireless communication terminal transmits dummy data while transmittingdata to the second wireless communication terminal. It is described withreference to FIGS. 16 and 17 that the second wireless communicationterminal transmits data to the first wireless communication terminal. Inparticular, it is described that the second wireless communicationterminal transmits dummy data together while transmitting data to thefirst wireless communication terminal.

FIG. 16 is a view illustrating that a plurality of stations transmitdata to an access point according to an embodiment of the presentinvention.

The first wireless communication terminal may transmit to the secondwireless communication terminal a trigger frame for triggering amultiple access for the first wireless communication terminal of thesecond wireless communication terminal. Specifically, the first wirelesscommunication terminal may transmit the trigger frame to the secondwireless communication terminal in each predetermined period. In anotherspecific embodiment, a trigger frame may be transmitted to the secondwireless communication terminal after a predetermined time elapses fromwhen a frame is received from the second wireless communicationterminal. At this time, the trigger frame may follow the format of theRTS frame. Specifically, the first wireless communication terminal mayset a value of an RA field indicating a reception address in an RTSframe to a specific address, and may transmit the RTS frame to aplurality of second wireless communication terminals. At this time, thespecific address may indicate uplink access and may be a predeterminedbroadcast address.

The second wireless communication terminal that receives the triggerframe may transmit data or transmit information required for channelallocation to the first wireless communication terminal. Specifically,after a predetermined time elapses from the transmission of the triggerframe, the second wireless communication terminal may transmit data ortransmit information required for channel allocation to the firstwireless communication terminal. At this time, the predetermined timemay be SIFS defined in the 802.11 standard.

Specifically, the second wireless communication terminal may transmitdata by using an orthogonal code in a code set including a plurality oforthogonal codes, or may transmit information required for receiving itsallocated channel to the first wireless communication terminal. In aspecific embodiment, the second wireless communication terminal mayaccess the first wireless communication terminal by using the orthogonalcode as the multiple access code. When the plurality of second wirelesscommunication terminals access the first wireless communication terminalby using different orthogonal codes, even if the plurality of secondwireless communication terminals use the same channel, the firstwireless communication terminal may extract an orthogonal component ofeach of the plurality of second wireless communication terminalsincluded in the signal through an auto-correlation operation. At thistime, a pattern of each orthogonal code appears in the extractedorthogonal component. Through this, the first wireless communicationterminal may simultaneously receive data from the plurality of secondwireless communication terminals connected through the same channel orreceive information required for channel allocation.

The orthogonal code set may be generated based on informationtransmitted by the first wireless communication terminal. For example,the second wireless communication terminal may receive a frame includinginformation on the orthogonal code set from the first wirelesscommunication terminal. At this time, the second wireless communicationterminal may obtain the orthogonal code based on the information on theorthogonal code set. Specifically, the information on the orthogonalcode set may be information on the base sequence used to generate theorthogonal code. Specifically, the information on the base sequence maybe an index indicating a base sequence.

In a specific embodiment, the second wireless communication terminal maytransmit data or transmit information required for channel allocation byusing an orthogonal code allocated to the second wireless communicationterminal in advance. At this time, the first wireless communicationterminal may allocate an orthogonal code corresponding to the secondwireless communication terminal as a association identifier foridentifying the association of the second wireless communicationterminal and the first wireless communication terminal. At this time,the association identifier may be an AID. In such a case, the secondwireless communication terminal may transmit data or informationrequired for receiving an allocated channel by using the associationidentifier as the orthogonal code.

In another specific embodiment, the second wireless communicationterminal may transmit data or transmit information required for channelallocation by randomly selecting any one orthogonal code from anorthogonal code set including a plurality of orthogonal codes. At thistime, the first wireless communication terminal may transmit informationfor identifying the first wireless communication terminal together whiletransmitting data or transmitting information required for channelallocation.

When the second wireless communication terminal transmits informationrequired for channel allocation, the first wireless communicationterminal allocates a channel to each of the plurality of second wirelesscommunication terminals on the basis of the information required forreceiving an allocated channel. At this time, the information requiredfor receiving an allocated channel may include information indicatingthe size of data to be transmitted by the second wireless communicationterminal. In addition, the information required for receiving anallocated channel may include an identifier for identifying the secondwireless communication terminal. At this time, the identifier foridentifying the second wireless communication terminal may be an AID ora partial AID that identifies a association with the first wirelesscommunication terminal. In addition, the information required forreceiving an allocated channel may include channel access mapinformation indicating a channel to be allocated to the second wirelesscommunication terminal. At this time, the channel access map informationmay include information on the idle channel detected by the secondwireless communication terminal.

The first wireless communication terminal transmits a frame indicatingan allocated channel to the second wireless communication. Specifically,the first wireless communication terminal may transmit a frameindicating an allocated channel to the second wireless communicationterminal through a channel allocated to the second wirelesscommunication terminal. At this time, the frame indicating the channelallocated to the second wireless communication terminal may includeinformation indicating the time that the second wireless communicationterminal is able to use for data transmission. At this time, the timeavailable for data transmission may be a time commonly applied to aplurality of second wireless communication terminals. Therefore, thetime available for data transmission may be determined based on thelongest time among the data transmission times of the plurality ofsecond wireless communication terminals. At this time, the timeavailable for data transmission may be transmitted as a duration fieldvalue of a frame indicating a channel allocated to the second wirelesscommunication terminal. Therefore, the duration field value of the frameindicating the channel allocated to the second wireless communicationterminal may be specified based on the time required for transmittingthe largest data among the transmission data of the plurality of secondwireless communication terminals. Also, the frame indicating the channelallocated to the second wireless communication terminal may be a CTSframe.

The second wireless communication terminal obtains information on thechannel allocated to the second wireless communication terminal based onthe frame indicating the channel allocated to the second wirelesscommunication terminal. When the frame indicating the channel allocatedto the second wireless communication terminal is a CTS frame, the secondwireless communication terminal determines a channel, through which aCTS frame using an identifier for identifying the second wirelesscommunication terminal itself as a reception address RA is transmitted,as a channel allocated to the second wireless communication terminalitself. At this time, the identifier for identifying the second wirelesscommunication terminal may be a Media Access Control (MAC) addresscorresponding to the AID of the second wireless communication terminal.

The second wireless communication terminal transmits data to the firstwireless communication terminal through the channel allocated to thesecond wireless communication terminal. At this time, the secondwireless communication terminal may transmit dummy data when there is aremaining time for transmitting the second wireless communicationterminal's own data. At this time, as described above, the dummy datarepresents meaningless data that is distinguished from meaningful datatransmitted through a data frame. Specifically, the dummy data may be acontinuous pattern of a specific value such as “0”. Specifically, thedummy data may be referred to as a busytone. In a specific embodiment,the second wireless communication terminal may transmit data and then,transmit the dummy data during a time for transmitting data after thedata frame transmission. The FCS field indicates whether an erroroccurs. Therefore, when the dummy data is transmitted before the FCSfield, the first wireless communication terminal should receive thedummy data until the FCS field is received and confirm whether the FCSfield is received. Therefore, in such a case, the first wirelesscommunication terminal may not stop an operation. Therefore, after thedata frame transmission, it may indicate after the FCS field of the dataframe is transmitted. At this time, as described above, the secondwireless communication terminal may obtain information on the time fortransmitting data from the frame indicating the channel allocated to thesecond wireless communication terminal. Specifically, the secondwireless communication terminal may obtain the time for transmittingdata from the duration field of the frame indicating the channelallocated to the second wireless communication terminal. It is possibleto prevent another wireless communication terminal from using acorresponding channel through such an operation of the second wirelesscommunication terminal. In addition, if the second wirelesscommunication terminal transmits dummy data after the data frametransmission, the first wireless communication terminal does not need toperform calculation on the data transmitted on a corresponding channelwhile the dummy data is transmitted. Therefore, the processing burden ofthe first wireless communication terminal may be reduced through such anoperation.

The first wireless communication terminal may transmit an ACK frame toeach of the plurality of second wireless communication terminals thattransmit data through a channel allocated to each of the plurality ofsecond wireless communication terminals. Specifically, after apredetermined time elapses from the reception of the last transmissioncompleted data frame, the first wireless communication terminaltransmits an ACK frame to a plurality of second wireless communicationterminals that transmit data through a channel allocated to each of theplurality of second wireless communication terminals. At this time, thepredetermined time may be SIFS defined in 802.11.

In an embodiment where the first wireless communication terminal doesnot transmit the trigger frame, the second wireless communicationterminal may access the first wireless communication terminal at apredetermined time point and transmit information required fortransmitting data or receiving an allocated channel.

In another specific embodiment, when the channel is idle for apredetermined time or longer, the second wireless communication terminalmay access the first wireless communication terminal to transmit data ortransmit information required for receiving an allocated channel. Then,the operations of the first wireless communication terminal and thesecond wireless communication terminal may be the same as thosedescribed above. Accordingly, description for this is omitted.

In the embodiment of FIG. 16, an access point AP transmits a triggerframe for triggering multiple uplink access to a plurality of stations.

The first station STA1, the second station STA2, the third station STA3,and the fourth station STA4, which receive a trigger frame, transmitinformation required for receiving an allocated channel to the accesspoint AP by using each different orthogonal code. At this time, asdescribed above, the information required for receiving an allocatedchannel includes at least one of information indicating the size of datato be transmitted by the second wireless communication terminal, anidentifier for identifying the second wireless communication terminal,and channel access map information indicating a channel to be allocatedto the second wireless communication terminal. At this time, the channelaccess map information may include information on the idle channeldetected by the second wireless communication terminal.

The access point AP performs an auto-correlation calculation on thereceived signal and obtains information required for channel allocationfrom a signal transmitted by each of the first station STA1, the secondstation STA2, the third station STA3, and the fourth station STA4. Atthis time, since the first station STA1, the second station STA2, thethird station STA3, and the fourth station STA4 all use differentorthogonal codes, the access point AP may identify a signal transmittedby each of the first station STA1, the second station STA2, the thirdstation STA3, and the fourth station STA4.

The access point AP allocates a channel to the first station STA1, thesecond station STA2, the third station STA3, and the fourth station STA4based on information required for channel allocation. At this time, theaccess point AP detects an idle channel and allocates the idle channelto the first station STA1, the second station STA2, and the thirdstation STA3. Specifically, the access point AP allocates a primarychannel Primary to the first station STA1, allocates a first secondarychannel Secondary 1 to the second station STA2, allocates a sixthsecondary channel Secondary 6 to the third station STA3, and allocates asecond secondary channel to the fourth station STA4.

The access point AP transmits a CTS frame through a channel allocated toeach of the first station STA1, the second station STA2, the thirdstation STA3, and the fourth station STA4.

Each of the first station STA1, the second station STA2, the thirdstation STA3, and the fourth station STA4 transmits data through achannel allocated to each of the first station STA1, the second stationSTA2, the third station STA3, and the fourth station STA4. At this time,the second station STA2, the third station STA3, and the fourth stationSTA4 transmit dummy data until the transmission of the first stationSTA1 is terminated after their data transmissions.

The access point AP receives data from each of the first station STA1,the second station STA2, the third station STA3, and the fourth stationSTA4, and transmits an ACK frame to each of the first station STA1, thesecond station STA2, the third station STA3, and the fourth stationSTA4. Specifically, from when receiving data from the first stationSTA1, the access point AP transmits an ACK frame to each of the firststation STA1, the second station STA2, the third station STA3, and thefourth station STA4 after SIFS.

FIG. 17 is a view illustrating that a plurality of stations transmitdata while reducing the processing burden of an access point accordingto an embodiment of the present invention.

The second wireless communication terminal may transmit dummy data aftertransmitting one frame to the first wireless communication terminal.Specifically, the first wireless communication terminal may transmitdummy data after transmitting the FCS field of any one data frame to thesecond wireless communication terminal. As described above, such dummydata may be referred to as a busytone. Specifically, the second wirelesscommunication terminal may transmit dummy data after transmitting aframe including information required for channel allocation to the firstwireless communication terminal. Also, the second wireless communicationterminal may transmit dummy data after transmitting the data frameincluding data to the first wireless communication terminal. In aspecific embodiment, the second wireless communication terminal maytransmit dummy data after a predetermined time elapses from when theframe is transmitted to the first wireless communication terminal. Atthis time, the predetermined time may be SIFS defined in 802.11. Throughthis, the first wireless communication terminal has a time forperforming an operation while dummy data is transmitted. In addition, itis possible to prevent another terminal not participating intransmission from accessing a corresponding channel.

The second wireless communication terminal may repeatedly transmit thesame frame to the first wireless communication terminal. Specifically,the second wireless communication terminal may transmit to the firstwireless communication terminal a frame including information forreceiving an allocated channel. Further, the second wirelesscommunication terminal may repeatedly transmit a frame including data tothe first wireless communication terminal. At this time, the firstwireless communication terminal may ignore the redundantly transmittedframes. Through this, the first wireless communication terminal has atime for performing an operation. In addition, it is possible to preventanother terminal not participating in transmission from accessing acorresponding channel.

In the embodiment of FIG. 17(A), the first station STA1, the secondstation STA2, the third station STA3, and the fourth station STA4transmit to an access point a frame including information required forreceiving an allocated channel by using each different code. At thistime, the first station STA1, the second station STA2, the third stationSTA3, and the fourth station STA4 further transmit a frame includinginformation required for receiving an allocated channel to the accesspoint AP twice (S1701). The access point AP ignores the second and thirdframes received after the frame including information required forreceiving an allocated channel from an access point that receives datafirst. Through this, the access point AP secures the calculation timerequired for allocating a channel to the first station STA1, the secondstation STA2, the third station STA3, and the fourth station STA4.

The access point AP transmits a CTS frame to each of the first stationSTA1, the second station STA2, the third station STA3, and the fourthstation STA4 through a channel allocated to each of the first stationSTA1, the second station STA2, the third station STA3, and the fourthstation STA4.

In the embodiment of FIG. 17(B), the first station STA1, the secondstation STA2, the third station STA3, and the fourth station STA4transmit to an access point a frame including information required forreceiving an allocated channel by using each different orthogonal code.

The first station STA1, the second station STA2, the third station STA3,and the fourth station STA4 transmit dummy data to the access point APafter transmitting a frame including information required for receivingan allocated channel (S1902). Specifically, the first station STA1, thesecond station STA2, the third station STA3, and the fourth station STA4transmit dummy data to the access point AP after SIFS from whentransmitting a frame including information required for receiving anallocated channel. Through this, the access point AP secures thecalculation time required for allocating a channel to the first stationSTA1, the second station STA2, the third station STA3, and the fourthstation STA4.

The access point AP transmits a CTS frame to each of the first stationSTA1, the second station STA2, the third station STA3, and the fourthstation STA4 through a channel allocated to each of the first stationSTA1, the second station STA2, the third station STA3, and the fourthstation STA4.

FIG. 18 is a view illustrating a basic service set including a pluralityof stations and an access point according to an embodiment of thepresent invention.

The first wireless communication terminal and each of the plurality ofsecond wireless communication terminals may be physically located at along distance from each other. In such a case, the first wirelesscommunication terminal may not detect an Overlapping Basic Service Set(OBSS) that affects each of the plurality of second wirelesscommunication terminals. Therefore, the idle state of a channel detectedby the first wireless communication terminal and each of the pluralityof second wireless communication terminals may be different. Therefore,when the first wireless communication terminal allocates a channel toeach of the plurality of second wireless communication terminals inconsideration of only the channel state detected by the first wirelesscommunication terminal itself, a channel where a collision with awireless communication terminal in another BSS is able to occur may beallocated to the plurality of second wireless communication terminals.Such a situation will be described with reference to the embodiment ofFIG. 18.

In the embodiment of FIG. 18, the access point AP detects the primarychannel Primary, the first secondary channel Secondary 1, the secondsecondary channel Secondary 2, and the third secondary channel Secondary3 as idle channels (1801). However, the first station STA1 is affectedby the first OBSS OBSS1, so that it detects the primary channel Primary,the fourth secondary channel Secondary 4, the fifth secondary channelSecondary 5, the sixth secondary channel Secondary 6, and the seventhsecondary channel Secondary 7 as idle channels (1802). In addition, thesecond station STA2 is affected by the second OBSS OBSS2, so that itdetects the primary channel Primary, the first secondary channelSecondary 1, the fifth secondary channel Secondary 5, the sixthsecondary channel Secondary 6, and the seventh secondary channelSecondary 7 as idle channels (1803). In addition, the third station STA3is affected by the third OBSS OBSS3, so that it detects the primarychannel Primary, the first secondary channel Secondary 1, the secondsecondary channel Secondary 2, the fifth secondary channel Secondary 5,and the sixth secondary channel Secondary 6 as idle channels (1804). Inaddition, the fourth station STA4 is affected by the fourth OBSS OBSS4,so that it detects the primary channel Primary, the first secondarychannel Secondary 1, the second secondary channel Secondary 2, the thirdsecondary channel Secondary 3, and the seventh secondary channelSecondary 7 as idle channels (1805).

At this point, when the access point AP allocates the first secondarychannel Secondary 1 to the first station STA1, allocates the secondsecondary channel Secondary 2 to the second station STA2, allocates theprimary channel Primary to the third station STA3, and allocates thesixth secondary channel Secondary 6 to the fourth station STA4, theremaining stations except for the third station STA3 may not use theallocated channels.

Therefore, the first wireless communication terminal should allocate achannel to each of the second wireless communication terminals inconsideration of the channel state detected by each of the plurality ofsecond wireless communication terminals. This will be described withreference to FIGS. 19 to 22.

FIG. 19 is a view illustrating that an access point transmits data to aplurality of stations by using a frame indicating that data istransmitted to a plurality of wireless communication terminals accordingto an embodiment of the present invention.

The first wireless communication terminal transmits to the plurality ofsecond wireless communication terminals a frame indicating that there isdata to be transmitted to the plurality of second wireless communicationterminals. The frame indicating that there is data to be transmitted tothe plurality of second wireless communication terminals may includeinformation for identifying the plurality of second wirelesscommunication terminals that are to receive data. The information foridentifying the plurality of second wireless communication terminals maybe a plurality of association identifiers for identifying each of theplurality of second wireless communication terminals. At this time, theassociation identifier is an identifier for identifying the associationof the first wireless communication terminal and the second wirelesscommunication terminal. Specifically, the association identifier may bean AID. In another specific embodiment, the AID may be a partial AID.For example, the association identifier may be the MAC address of thesecond wireless communication terminal corresponding to the AID. Inaddition, the frame indicating that there is data to be transmitted to aplurality of second wireless communication terminals may include a GroupAddress for identifying a group including the second wirelesscommunication terminals.

The frame indicating that there is data to be transmitted to theplurality of second wireless communication terminals may be one obtainedby extending the legacy RTS frame. Specifically, a field located at theposition of a receiver address field of an legacy RTS frame in a frameindicating that there is data to be transmitted to the second wirelesscommunication terminal includes a group identifier for identifying agroup including a plurality of second wireless communication terminalsthat are to receive data. In addition, the frame indicating that thereis data to be transmitted to the plurality of second wirelesscommunication terminals may include an extension field for extending anRTS frame. At this time, the extension field may be located after theFCS field of the legacy RTS frame. In addition, the extension field mayinclude information for identifying each of the plurality of secondwireless communication terminals. In a specific embodiment, when a frameindicating that there is data to be transmitted to a plurality of secondwireless communication terminals is used for a channel having abandwidth of 160 MHz, the extension field may include the addresses andpartial AIDs of a maximum of 32 second wireless communication terminals.

The second wireless communication terminal may determine whether data isto be transmitted to the second wireless communication terminal based onthe frame indicating that there is data to be transmitted to theplurality of second wireless communication terminals. Specifically, thesecond wireless communication terminal determines whether data istransmitted to the second wireless communication terminal according towhether the frame indicating that there is data to be transmitted to theplurality of second wireless communication terminals includesinformation for identifying the second wireless communication terminal.

The second wireless communication terminal determining that data is tobe transmitted accesses the first wireless communication terminal. Atthis time, the first wireless communication terminal may designate aplurality of access methods to allow the plurality of second wirelesscommunication terminals to make an access by using a predeterminedcommunication method. At this time, the access method may be related toat least one of an access time point, an orthogonal code used foraccess, and a channel used for access. In such a case, the secondwireless communication terminal may access the first wirelesscommunication terminal through any one of a plurality of designatedaccess methods.

Specifically, the first wireless communication terminal may designate anorthogonal code set that the plurality of second wireless communicationterminals access. Accordingly, the second wireless communicationterminal may access the first wireless communication terminal by usingany one orthogonal code in the orthogonal code set.

In a specific embodiment, another base sequence that is guaranteed to beorthogonal to an adjacent BSS is allocated to BSS. For example, theplurality of base sequences may be allocated to the plurality of BSSs,respectively. At this time, the first wireless communication terminaland the second wireless communication terminal may receive an indexindicating the allocated base sequence. The first wireless communicationterminal and the second wireless communication terminal may obtain abase sequence according to the index indicating the received basesequence. In a specific embodiment, when the BSS uses eight channels ina 20 MHz unit, the length of the base sequence may be eight or more. Thelength of the base sequence may be longer for stable zeroauto-correlation characteristics. Through this, the first wirelesscommunication terminal and the second wireless communication terminalmay minimize base sequence interference between adjacent BSSs. Also, ina specific embodiment, the base sequence may be generated by aZadoff-Chu sequence that satisfies Constant Amplitude Zero AutoCorrelation (CAZAC) characteristics.

The first wireless communication terminal and the second wirelesscommunication terminal may generate a plurality of orthogonal codesincluded in the orthogonal code set based on the allocated basesequence. Specifically, the first wireless communication terminal andthe second wireless communication terminal may generate a plurality oforthogonal codes included in the orthogonal code set by cyclic-shiftingthe allocated base sequence.

The first wireless communication terminal may allocate a plurality oforthogonal codes included in the orthogonal code set to a plurality ofsecond wireless communication terminals, respectively. Accordingly, thesecond wireless communication terminal may access the first wirelesscommunication terminal by using the orthogonal code allocated to thesecond wireless communication terminal. At this time, the secondwireless communication terminal may obtain an orthogonal code allocatedto the second wireless communication terminal based on the frameindicating that there is data to be transmitted to the plurality ofsecond wireless communication terminals. Specifically, the secondwireless communication terminal may obtain an orthogonal code allocatedto the second wireless communication terminal according to thearrangement order of second wireless communication terminal identifiersin the frame indicating that there is data to be transmitted to theplurality of second wireless communication terminals. For this, thesecond wireless communication terminal may receive information on a basesequence and a code set based on the base sequence during a associationprocess with the first wireless communication terminal. The informationon the base sequence may be an index indicating a base sequence. In aspecific embodiment, the orthogonal codes in the code set may be 32. Forexample, the second wireless communication terminal may receive an indexindicating a base sequence and a total of 32 orthogonal codes generatedby cyclic-shifting the base sequence during the association process withthe first wireless communication terminal. When it is assumed that thesecond wireless communication terminal identifier is aligned in theseventh order in the frame indicating that there is data to betransmitted to the plurality of second wireless communication terminals,the second wireless communication terminal may obtain the seventhorthogonal code among the 32 orthogonal codes as the orthogonal codeallocated to the second wireless communication terminal.

In another specific embodiment, the second wireless communicationterminal may access the first wireless communication terminal byrandomly selecting any one of the plurality of orthogonal codes. In sucha case, since the first wireless communication terminal is not able toidentify the second wireless communication terminal through theorthogonal code, the second wireless communication terminal transmitsinformation for identifying the second wireless communication terminalwhile accessing the first wireless communication terminal.

When a plurality of second wireless communication terminals areconnected using different orthogonal codes, orthogonality is maintainedbetween orthogonal codes. Accordingly, the first wireless communicationterminal may obtain the orthogonal code included in an access signalthrough the auto-correlation operation. Specifically, the first wirelesscommunication terminal may perform an auto-correlation operation on thereceived signal to obtain a base sequence and a signal pattern obtainedby cyclic-shifting the base sequence. The first wireless communicationterminal may determine the orthogonal code included in the access signalby comparing the cyclic shift position where a peak value included inthe obtained signal pattern appears with a plurality of orthogonal codesincluded in the code set. Through this, the wireless communicationterminal may recognize that the second wireless communication terminal,to which the obtained orthogonal code is allocated, accesses the firstwireless communication terminal.

At this time, the second wireless communication terminal may transmitinformation on the idle channel detected by the second wirelesscommunication terminal to the first wireless communication terminal.Specifically, the second wireless communication terminal may access thefirst wireless communication terminal through all the idle channelsdetected as the channel access idle channel by the second wirelesscommunication terminal.

The first wireless communication terminal allocates a frequency band toeach of the plurality of second wireless communication terminals thataccess the first wireless communication terminal. Specifically, thefirst wireless communication terminal transmits may allocate a channelto each of the plurality of second wireless communication terminals,based on the information on a channel detected as an idle channel by thefirst wireless communication terminal and an idle channel detected byeach of the plurality of second wireless communication terminals. In aspecific embodiment, the first wireless communication terminal mayallocate to the second wireless communication terminal a channel that isdetected as an idle channel by the first wireless communication terminaland accessed by detecting a corresponding channel as an idle channel bythe second wireless communication. In addition, the first wirelesscommunication terminal may allocate a frequency band to each secondwireless communication terminal by a sub-channel unit that is asub-channel of a channel. At this time, the frequency bandwidth of thechannel may be 20 MHz and the bandwidth of the sub-channel may be 5 MHz.

The first wireless communication terminal transmits a frame indicating achannel allocated to the second wireless communication terminal to thesecond wireless communication terminal. As described above, the channelallocated to the second wireless communication terminal may be asub-channel. A specific format of a frame indicating a channel allocatedto the second wireless communication terminal will be described laterwith reference to FIG. 20.

The second wireless communication terminal transmits a frame indicatingready to receive data to the first wireless communication terminal. Thesecond wireless communication terminal may transmit a frame indicatingready to receive data to the first wireless communication terminalthrough a channel allocated to the second wireless communicationterminal. When receiving an allocated sub-channel, the second wirelesscommunication terminal transmits to the first wireless communicationterminal a frame indicating ready to receive data through the channelhaving a corresponding sub-channel as a sub-band. Specifically, aplurality of second wireless communication terminals that receiveallocated sub-channels included in the same channel may sequentiallytransmit frames indicating ready to receive data. In a specificembodiment, a plurality of second wireless communication terminals thatreceive allocated sub-channels included in the same channel maysequentially transmit frames indicating ready to receive data accordingto a round-robin method. Especially, the second wireless communicationterminal may transmit to the first wireless communication terminal aframe indicating ready to receive data through the channel having acorresponding sub-channel as a sub-band. At this time, the order oftransmitting a frame indicating ready to receive data from the secondwireless communication terminal to the first wireless communicationterminal may be an arrangement order of information on a channelallocated to the second wireless communication terminal included in theframe indicating a channel allocated to the second wirelesscommunication terminal. Specifically, when the frame indicating thechannel allocated to the second wireless communication terminal includesinformation on the channel allocation in the order of the firstsub-channel and the second sub-channel, the second wirelesscommunication terminal that receives the allocated first sub-channel maytransmit a frame indicating ready to receive data to the first wirelesscommunication terminal, and the second wireless communication terminalthat receives the allocated second sub-channel may transmit a frameindicating ready to receive data to the first wireless communicationterminal.

The first wireless communication terminal transmits data to the secondwireless communication terminal through the channel allocated to thesecond wireless communication terminal. Specifically, the first wirelesscommunication terminal may transmit data to the second wirelesscommunication terminal through the above-described embodiments. Also,the first wireless communication terminal may transmit data to thesecond wireless communication terminal through a method other than theabove-described embodiment.

The second wireless communication terminal transmits a frame indicatingwhether data is received to the first wireless communication terminalthrough a channel allocated to the second wireless communicationterminal. At this point, the frame indicating whether data is receivedmay be the above-described sACK frame.

Also, the first wireless communication terminal may receive a frameindicating whether data is to be received from the second wirelesscommunication terminal, and transmit an ACK-to-Self frame indicating theACK frame indicating that the reception address is the first wirelesscommunication terminal. In particular, when allocating a frequency bandto the second wireless communication terminal by a sub-channel unit, thefirst wireless communication terminal may transmit the ACK-to-Selfframe.

In the embodiment of FIG. 19, the access point AP transmits a frameindicating that there is data to be transmitted to the plurality ofsecond wireless communication terminals to the first station STA1 to thesixteenth station STA16 (S1901). At this time, a frame indicating thatthere is data to be transmitted to a plurality of second wirelesscommunication terminals may include a partial AID of a plurality ofstations that are to receive data or the MAC addresses of a plurality ofstations to receive data. In addition, the frame indicating that thereis data to be transmitted to a plurality of second wirelesscommunication terminals may follow the format of the RTS frame.

The first to sixteenth stations STA1 to STA16 access the access point APbased on the allocated orthogonal code (S1902). At this time, the firstto sixteenth stations STA1 to STA16 access the access point AP throughdifferent orthogonal codes. Specifically, as in the above-describedembodiment, the first to sixteenth stations STA1 to STA16 may access theaccess point AP through all of the channels detected as idle channels bythe first to sixteenth stations STA1 to STA16.

The access point AP obtains the orthogonal code included in an accesssignal through the auto-correlation operation. Since the relationshipbetween an orthogonal code and a station that receives an allocatedorthogonal code is known, the access point AP may determine whichstation accesses the access point AP.

The access point AP transmits an sRTS frame, which is a frame indicatinga channel allocated to the second wireless communication terminal, toeach of the first to sixteenth stations STA1 to STA16 that access theaccess point AP (S1903). Specifically, the access point AP transmits ansRTS frame to each of the first to sixteenth stations STA1 to STA16through a sub channel allocated to each of the first to sixteenthstations STA1 to STA16.

The first to sixteenth stations transmit a CTS frame indicating ready toreceive data sequentially through a channel having a sub-channelallocated to each of the first to sixteenth stations as a sub-band(S1904). Specifically, the first to fourth stations STA1 to STA4sequentially transmit CTS frames through the first band (20 MHz band1).In addition, the fifth station STA5 to the eighth station STA8sequentially transmit the CTS frames through the second band (20 MHzband2). In addition, the ninth station STA9 to the twelfth station STA12sequentially transmit the CTS frames through the third band (20 MHzband2). In addition, the thirteenth station STA13 to the sixteenthstation STA16 sequentially transmit the CTS frames through the fourthband (20 MHz band4).

The access point AP transmits data to the first station STA1 to thesixteenth station STA16 (S1905). Specifically, the access point AP maytransmit data to the first station STA1 to the sixteenth station STA16according to the above-described embodiment. In addition, the accesspoint AP may transmit data to the first station STA1 to the sixteenthstation STA16 through a method other than the above-describedembodiment.

Each of the first station STA1 to the sixteenth station STA16 transmitsan sACK frame indicating whether data is received through a channelallocated to each of the first station STA1 to the sixteenth stationSTA16 (S1906).

The access point AP that receives the sACK frame transmits theabove-described ACK-to-Self frame (S1907). Through this, compatibilitywith wireless communication terminals that do not support embodiments ofthe present invention is secured.

It is described in the above-described embodiment that the firstwireless communication terminal specifies an access method. At thistime, the first wireless communication terminal may specify a channel tobe used to access the first wireless communication terminal by thesecond wireless communication terminal. This will be described withreference to FIG. 20.

FIG. 20 is a view illustrating the format of a frame indicating achannel to be used to access a first wireless communication terminal bya second wireless communication terminal according to an embodiment ofthe present invention.

The first wireless communication terminal may transmit a frame, whichindicates a channel to be used to access the first wirelesscommunication terminal by the second wireless communication terminal, tothe second wireless communication terminal. The frame indicating achannel to be used to access the first wireless communication terminalby the second wireless communication terminal may include access channelinformation that is information on a channel accessible by the secondwireless communication terminal. Specifically, the access channelinformation may include information about an index indicating a channelto which the second wireless communication terminal is able to access.For example, the access channel information may include information onan index indicating a plurality of channels and information indicatingwhether it is possible to access a channel indicated by a correspondingindex.

The second wireless communication terminal receives a frame indicating achannel to be used to access the first wireless communication terminalby the second wireless communication terminal. The second wirelesscommunication terminal may access any one of the plurality of channelsbased on a frame indicating a channel to be used to access the firstwireless communication terminal by the second wireless communicationterminal. Specifically, the second wireless communication terminal mayobtain access channel information from a frame indicating a channel tobe used to access the first wireless communication terminal by thesecond wireless communication terminal. The second wirelesscommunication terminal may access any one of a plurality of accessiblechannels according to the access channel information. Specifically, thesecond wireless communication terminal may randomly access any one of aplurality of accessible channels according to the obtained accesschannel information. According to another embodiment of the presentinvention, the second wireless communication terminal may access all thechannels detected as idle channels among a plurality of accessiblechannels according to the access channel information obtained through anidle channel.

In a specific embodiment, the frame indicating a channel to be used toaccess the first wireless communication terminal by the second wirelesscommunication terminal may be identical to the frame indicating thatthere is data to be transmitted to the plurality of second wirelesscommunication terminals.

In another specific embodiment, the frame indicating a channel to beused to access the first wireless communication terminal by the secondwireless communication terminal may be different from the frameindicating that there is data to be transmitted to the plurality ofsecond wireless communication terminals. At this time, aftertransmitting to a plurality of second wireless communication terminals aframe indicating that there is data to be transmitted to the secondwireless communication terminal, the first wireless communicationterminal may transmit to the plurality of second wireless communicationterminals a frame indicating a channel to be used to access the firstwireless communication terminal by the second wireless communicationterminal.

In the embodiment of FIG. 20, a frame indicating a channel to be used toaccess the first wireless communication terminal by the second wirelesscommunication terminal may include a Frame Control field indicatinginformation on frame control.

In addition, the frame indicating a channel to be used to access thefirst wireless communication terminal by the second wirelesscommunication terminal may include a Duration field indicatinginformation for NAV setting.

In addition, the frame indicating a channel to be used to access thefirst wireless communication terminal by the second wirelesscommunication terminal may include a Receiver Address field indicatingthe address of the second wireless communication terminal that receivesthe frame. At this time, the Receiver Address field may include a Prefixfield indicating the address of the second wireless communicationterminal that receives a frame and a Band Indication field indicating achannel that the second wireless communication terminal is able toaccess. At this time, the Prefix field may have a value of a groupaddress indicating the plurality of second wireless communicationterminals. In addition, the Band Indication field may include aplurality of bits indicating whether each of the plurality of channelsis able to access. In a specific embodiment, the Band Indication fieldmay include eight bits. At this time, the first bit of the BandIndication field indicates whether primary channel Primary is able toaccess. In addition, the second to eighth bits of the Band Indicationfield indicate whether the first secondary channel Secondary 1 to theseventh secondary channel Secondary 7 are able to access. For example,when the primary channel Primary, the first secondary channel Secondary1, the second secondary channel Secondary 2, and the third secondarychannel Secondary 3 are available channels, the values of the first,second, and third bits in the Band Indication field are 1s. Therefore,the value of the Band Indication field is 240(11110000b).

In addition, the frame indicating a channel to be used to access thefirst wireless communication terminal by the second wirelesscommunication terminal may include a Transmitter Address fieldindicating the address of the first wireless communication terminal thattransmits the frame.

In addition, the frame indicating a channel to be used to access thefirst wireless communication terminal by the second wirelesscommunication terminal may include an FCS field indicating whether anerror occurs.

FIG. 21 is a view illustrating a structure of an extension field of aframe indicating that there is data to be transmitted to a plurality ofsecond wireless communication terminals according to an embodiment ofthe present invention.

As described above, the frame indicating that there is data to betransmitted to a plurality of second wireless communication terminalsmay include a plurality of second wireless communication terminalidentifiers for identifying each of the plurality of second wirelesscommunication terminals. At this time, the second wireless communicationidentifier may be an association identifier for identifying theassociation of the first wireless communication terminal and the secondwireless communication terminal. Specifically, the associationidentifier may be an AID. At this time, the association identifier maybe a Partial AID. In another specific embodiment, the second wirelesscommunication terminal identifier may be a MAC address. Whentransmission for four second wireless communication terminals isavailable in each of eight bandwidths, a frame indicating that there isdata to be transmitted to a plurality of second wireless communicationterminals may include not more than 32 second wireless communicationterminal identifiers.

In a specific embodiment, a frame indicating that there is data to betransmitted to a plurality of second wireless communication terminalsmay have a format in which an extension field located after the FCSfield of an existing RTS frame in an existing RTS frame is added. Atthis time, the extension field includes a plurality of second wirelesscommunication terminal identifiers for identifying each of the pluralityof second wireless communication terminals.

In the embodiment of FIG. 21, the extension field includes a lengthfield indicating the length of the extension field.

Also, the extension field may include a Receiver Address fieldindicating an identifier for identifying a plurality of second wirelesscommunication terminals that are to receive data.

Also, the extension field may include a Padding field indicating paddingdata for adjusting the total length of the extension field in an octetunit.

In addition, the extension field may include an FCS field indicatingwhether the extension field includes an error.

Through the frame indicating that there is data to be transmitted to theplurality of second wireless communication terminals, the first wirelesscommunication terminal may efficiently inform that there is data to betransmitted to the plurality of second wireless communication terminals.

FIG. 22 is a view illustrating that an access point transmits data to aplurality of stations by using a frame indicating that data istransmitted to a plurality of wireless communication terminals accordingto another embodiment of the present invention.

As described above, a plurality of second wireless communicationterminals, which receive each of a plurality of allocated sub-channelsof the same channel, may sequentially transmit a frame indicating readyto receive data to the first wireless communication terminal. At thistime, the first wireless communication terminal may wait for apredetermined time to receive a frame indicating ready to receive data.After a predetermined time elapses, the first wireless communicationterminal transmits data based on whether a frame indicating ready toreceive data is prepared. At this time, the predetermined time may be atime required for transmitting a frame indicating that the firstwireless communication terminal is ready to receive data as much as thenumber of the second wireless communication terminals that allocate achannel. For example, when a frame indicating that the first wirelesscommunication terminal allocates a channel to two second wirelesscommunication terminals and the first wireless communication terminal isready to receive data is a CTS frame, the first wireless communicationterminal may wait until each of the two second wireless communicationterminals transmits the CTS frame.

At this time, if a smaller number of the second wireless communicationterminals are allocated to any one channel than another channel, whilethe first wireless communication terminal waits to receive a frameindicating ready to receive data from another channel, a correspondingchannel may be an idle state. Therefore, another wireless communicationterminals not participating in transmission may access a correspondingchannel. In order to prevent this, the second wireless communicationterminal that receives an allocated channel may transmit dummy datathrough a corresponding channel while the first wireless communicationterminal waits to receive a frame indicating ready to receive data fromanother channel. At this time, the second wireless communicationterminal may transmit dummy data to the first wireless communicationterminal or a predetermined address. In another specific embodiment, thesecond wireless communication terminal that receives a correspondingallocated channel may again transmit a frame indicating ready to receivedata through a corresponding channel while the first wirelesscommunication terminal wait to receive a frame indicating ready toreceive data from another channel. At this time, the second wirelesscommunication terminal may transmit a frame indicating ready to receivedata to the first wireless communication terminal or a predeterminedaddress.

For this, the second wireless communication terminal should know thenumber of the second wireless communication terminals that receive acorresponding allocated channel. In a specific embodiment, in order todetermine the number of the second wireless communication terminals thatreceive a corresponding allocated channel, the second wirelesscommunication terminal may monitor all the frequency bands used by thefirst wireless communication terminal. Specifically, the second wirelesscommunication terminal may determine the number of the second wirelesscommunication terminals that receive a corresponding allocated channelbased on the number of frames indicating a channel allocated to thesecond wireless communication terminal, which are transmitted through acorresponding channel. In another specific embodiment, the frameindicating a channel allocated to the second communication terminal mayinclude information on the number of the second wireless communicationterminals allocated to the corresponding channel. At this time, thesecond wireless communication terminal may determine the number of thesecond wireless communication terminals allocated to a correspondingchannel based on the frame indicating the channel allocated to thesecond communication terminal.

In addition, the second wireless communication terminal may receive dataand transmit a Block ACK frame as a frame indicating whether data isreceived. At this time, the block ACK frame is a frame indicatingwhether a plurality of data frames are received. Specifically, theplurality of second wireless communication terminals, which respectivelyreceive a plurality of allocated sub-channels of the same channel, maysequentially transmit block ACK frames to the first wirelesscommunication terminal through a corresponding channel. At this time,the order of transmitting a block ACK frame from the second wirelesscommunication terminal to the first wireless communication terminal maybe an arrangement order of information on a channel allocated to thesecond wireless communication terminal included in the frame indicatingthe allocated channel received by the second wireless communicationterminal. Specifically, when the frame indicating the channel allocatedto the second wireless communication terminal includes information onthe channel allocation in the order of the first sub-channel and thesecond sub-channel, the second wireless communication terminal thatreceives the allocated first sub-channel may transmit a block ACK frameto the first wireless communication terminal, and the second wirelesscommunication terminal that receives the allocated second sub-channelmay transmit a block ACK frame to the first wireless communicationterminal. The second wireless communication terminal may transmit ablock ACK frame through a band having a bandwidth of 20 MHz. In such acase, the first wireless communication terminal may not transmit anACK-to-Self frame in order for compatibility with a wirelesscommunication terminal that does not support the embodiment of thepresent invention. Also, according to a specific situation, a timerequired for transmitting a Block ACK frame by the second wirelesscommunication terminal may be less than a time required for transmittingan sACK frame by the second wireless communication terminal.

In the embodiment of FIG. 22, the access point AP transmits data to thefirst station STA1 to the seventh station STA7. The operations that thefirst to seventh stations STA1 to STA7 access the access point AP andreceive an sRTS frame indicating a channel allocated to the first toseventh stations STA1 to STA7 are identical to those of the embodimentof FIG. 19. Therefore, a detailed description thereof will be omitted.

The first to seventh stations STA1 to STA7 transmit a CTS frameindicating ready to receive data to the access point AP. Specifically,the first station STA1 and the second station STA2 sequentially transmitCTS frames to the access point AP through a first band (20 MHz band1)including a sub-band allocated to the first station STA1 and the secondstation STA2. In addition, the third station STA3 and the fourth stationSTA4 sequentially transmit CTS frames to the access point AP through asecond band (20 MHz band2) including a sub-band allocated to the thirdstation STA3 and the fourth station STA4. In addition, the sixth stationSTA6 and the seventh station STA7 sequentially transmit CTS frames tothe access point AP through a fourth band (20 MHz band4) including asub-band allocated to the sixth station STA6 and the seventh stationSTA7. At this time, the fifth station STA5 receives an allocated thirdband (20 MHz band 3) alone. Therefore, the fifth station STA5 transmitsa CTS frame to the access point AP through the third band (20 MHzband3). Then, while the access point AP receives the CTS frametransmitted by the other stations, the fifth station STA5 transmitsdummy data or a CTS frame again through the third band (20 MHz band3).Through this, the fifth station STA5 prevents another wirelesscommunication terminal from accessing the third band (20 MHz band3).

The access point AP transmits data to the first station STA1 to theseventh station STA7 that transmit the CTS frame. The access point APmay transmit data to the first station STA1 to the seventh station STA7through the above-described embodiments. In addition, the access pointAP may transmit data to the first station STA1 to the seventh stationSTA7 through a method other than the above-described embodiment.

The first station STA1 to the seventh station STA7 transmit a block ACKframe indicating whether data is received to the access point AP.Specifically, the first station STA1 and the second station STA2sequentially transmit block ACK frames to the access point AP through afirst band (20 MHz band1) including a sub-band allocated to the firststation STA1 and the second station STA2. In addition, the third stationSTA3 and the fourth station STA4 sequentially transmit block ACK framesto the access point AP through a second band (20 MHz band2) including asub-band allocated to the third station STA3 and the fourth stationSTA4. In addition, the sixth station STA6 and the seventh station STA7sequentially transmit block ACK frames to the access point AP through afourth band (20 MHz band4) including a sub-band allocated to the sixthstation STA6 and the seventh station STA7. In addition, the fifthstation STA5 transmits a block ACK frame to the access point AP throughthe third band (20 MHz band3).

FIG. 23 is a ladder diagram illustrating an operation that a firstwireless communication terminal transmits data to a second wirelesscommunication terminal according to an embodiment of the presentinvention.

The first wireless communication terminal 400 transmits a frameindicating that there is data to be transmitted to the second wirelesscommunication terminal 500 (S2301). Specifically, the frame indicatingthat there is data to be transmitted may be a frame indicating thatthere is data to be transmitted to a plurality of second wirelesscommunication terminals 500. At this time, the frame indicating thatthere is data to be transmitted to the plurality of second wirelesscommunication terminals 500 may include a plurality of identifiers foridentifying each of the plurality of second wireless communicationterminals 500 that are to receive the data. At this time, the identifiermay be a connection identifier for identifying the connection betweenthe first wireless communication terminal 400 and the second wirelesscommunication terminal 500. In addition, the connection identifier maybe AID. In addition, the connection identifier may be a partial AIDindicating a part of the entire AID. In another specific embodiment, theidentifier may be a MAC address. In addition, the frame indicating thatthere is data to be transmitted to the plurality of second wirelesscommunication terminals 500 may include a group identifier foridentifying a group indicating the plurality of second wirelesscommunication terminals 500 that are to receive the data. In addition,in a specific embodiment, the format of the frame indicating that thereis data to be transmitted may be a modification of the format of theexisting RTS frame as described above

The first wireless communication terminal 400 may transmit a frameindicating a method of accessing the first wireless communicationterminal 400 to the second wireless communication terminal 500. Theframe indicating an access method may include information on at leastone of an access time point, an orthogonal code used for access, and achannel used for access. In addition, the frame indicating an accessmethod may include information on a plurality of methods of accessingthe first wireless communication terminal 500. In addition, the frameindicating a method of accessing the first wireless communicationterminal 400 may be the same as the frame indicating that there is datato be transmitted. In another specific embodiment, the frame indicatinga method of accessing the first wireless communication terminal 400 maybe separated from the frame indicating that there is data to betransmitted.

At this time, the second wireless communication terminal 500 may accessthe first wireless communication terminal 400 through a methoddesignated by the first wireless communication terminal 400. Inaddition, the second wireless communication terminal 500 may randomlyselect any of a plurality of methods designated by the first wirelesscommunication terminal 400 and access the first wireless communicationterminal 400. Specifically, the second wireless communication terminal500 may randomly select any one of accessible channels indicated by aframe indicating an access method and access it. Also, the secondwireless communication terminal 500 may access the first wirelesscommunication terminal 400 through all the channels detected as idlechannels by using a method designated by the first wirelesscommunication terminal 400.

The first wireless communication terminal 400 may transmit a frameindicating a channel allocated to the second wireless communicationterminal 500 to the second wireless communication terminal 500.Specifically, the first wireless communication terminal 400 may transmita frame indicating a channel allocated to the second wirelesscommunication terminal to the second wireless communication terminal 500accessing the first wireless communication terminal 400. At this time, achannel allocated to a second wireless communication terminal mayindicate a channel and also a sub-channel that is the sub-band of thechannel. In addition, the frame indicating the channel allocated to thesecond wireless communication terminal may include information on theorder in which the second wireless communication terminal uses theallocated channel. In a specific embodiment, the frame indicating thechannel allocated to the second wireless communication terminal mayinclude information that the second wireless communication terminal usesthe allocated channel firstly or secondly. At this time, the informationon whether the allocated channel is used firstly or secondly by acorresponding second wireless communication terminal may be in a 1-bitflag format. As described above, in a specific embodiment, the frameindicating the channel allocated to the second wireless communicationterminal may be referred to as an sRTS frame.

The second wireless communication terminal 500 transmits to the firstwireless communication terminal 400 a frame indicating ready to receivedata based on a frame indicating that there is data to be transmitted(S2303). Specifically, when the frame indicating that there is data tobe transmitted includes the identifier of the second wirelesscommunication terminal 500, the second wireless communication terminal500 may transmit a frame indicating ready to receive data to the firstwireless communication terminal 400. Also, the second wirelesscommunication terminal 500 may transmit a frame indicating ready toreceive data to the first wireless communication terminal 400 through achannel allocated to the second wireless communication terminal 500.When receiving an allocated sub-channel, the second wirelesscommunication terminal 500 may transmit to the first wirelesscommunication terminal 400 a frame indicating ready to receive datathrough a channel having a corresponding sub-channel as a sub-band.Specifically, the plurality of second wireless communication terminals500 that receive allocated sub-channels included in the same channel maysequentially transmit frames indicating ready to receive data. In aspecific embodiment, the plurality of second wireless communicationterminals 500 that receive allocated sub-channels included in the samechannel may sequentially transmit frames indicating ready to receivedata according to a round-robin method. In addition, the order oftransmitting a frame indicating ready to receive data from the secondwireless communication terminal 500 to the first wireless communicationterminal 400 may be an arrangement order of information on a channelallocated to the second wireless communication terminal 500 included inthe frame indicating a channel allocated to the second wirelesscommunication terminal 500. Specifically, when the frame indicating thechannel allocated to the second wireless communication terminal 500includes information on the channel allocation in the order of the firstsub-channel and the second sub-channel, the second wirelesscommunication terminal 500 that receives the allocated first sub-channelmay first transmit a frame indicating ready to receive data to the firstwireless communication terminal 400. Then, the second wirelesscommunication terminal 500 that receives the second sub-channel maytransmit a frame indicating ready to receive data to the first wirelesscommunication terminal 400.

The first wireless communication terminal 400 transmits data to thesecond wireless communication terminal 500 (S2305). Accordingly, thesecond wireless communication terminal 500 may receive data from thefirst wireless communication terminal 400 based on the frame indicatingthat there is data to be transmitted. Specifically, when the frameindicating that there is data to be transmitted indicates that there isdata to be transmitted to the plurality of second wireless communicationterminal 500 and includes the identifier of the second wirelesscommunication terminal 500, the second wireless communication terminal500 identified by the identifier may receive data from the firstwireless communication terminal 400. In a specific embodiment, the firstwireless communication terminal 400 may transmit data to the secondwireless communication terminal 500 that transmits a frame indicatingready to receive the data. At this time, the first wirelesscommunication terminal 400 may use a plurality of RF chains for theplurality of respective second wireless communication terminals 500. Inanother specific embodiment, the first wireless communication terminal400 may group a plurality of second wireless communication terminals 500into a plurality of groups, and allocate one RF-chain to one groupincluding the plurality of second wireless communication terminals 500.At this time, the first wireless communication terminal 400 may groupthe second wireless communication terminals 500 based on a datatransmission time required for each of the plurality of second wirelesscommunication terminals 500. More specifically, when the difference intime required for data transmission to each of the plurality of secondwireless communication terminals 500 is within a reference value, thefirst wireless communication terminal 400 may group the plurality ofsecond wireless communication terminals 500 into one group. In anotherspecific embodiment, the first wireless communication terminal 400 maygroup the plurality of second wireless communication terminals 500 basedon the size of data to be transmitted to each of the plurality of secondwireless communication terminals 500. Specifically, when the differencein the size of data to be transmitted to each of the plurality of secondwireless communication terminals 500 is within a reference value, thefirst wireless communication terminal 400 may group the plurality ofsecond wireless communication terminals 500 into one group.

The first wireless communication terminal 400 may transmit data to theplurality of second wireless communication terminals 500 by varying achannel access method of each of the plurality of RF-chains.Specifically, the first wireless communication terminal 400 may occupy achannel according to a predetermined period, with respect to a channelincluded in the first RF-chain among the plurality of RF-chains. Inaddition, with respect to a channel included in the second RF-chain, thefirst wireless communication terminal 400 may detect whether acorresponding channel is idle and occupy a channel through a contentionprocedure. In a specific embodiment, the first wireless communicationterminal 400 may occupy a channel through a PCF included in the firstRF-chain among the plurality of RF-chains and occupy a channel includedin the second RF-chain through a DCF.

Before all the data transmissions for a plurality of second wirelesscommunication terminals 500 using one RF-chain are completed, the firstwireless communication terminal 400 may transmit dummy data to any oneof the second wireless communication terminals 500 that complete thetransmission. At this time, the dummy data represents meaningless datathat is distinguished from meaningful data transmitted through a dataframe. Specifically, the dummy data may be a continuous pattern of aspecific value such as “0”. Specifically, the first wirelesscommunication terminal 400 may transmit data to the second wirelesscommunication terminal 500 after the transmission of a data frame.Specifically, the first wireless communication terminal 400 may transmitdummy data to the second wireless communication terminal 500 aftertransmitting the FCS field of a data frame. In a specific embodiment,the dummy data may be referred to as a busytone. At this time, thesecond wireless communication terminal 500 may ignore the dummy data.

In another specific embodiment, the first wireless communicationterminal 400 may repeatedly transmit data to any one second wirelesscommunication terminal 500 that completes transmission before all thedata transmissions for the plurality of second wireless communicationterminals are completed. At this time, the first wireless communicationterminal 400 may transmit the same data again after transmitting thedata frame to the second wireless communication terminal 500.Specifically, the first wireless communication terminal 400 may againtransmit the same data frame to the second wireless communicationterminal 500 after transmitting the FCS field of the data frame. At thistime, the second wireless communication terminal 500 may ignore thetransmitted data repeatedly.

The first wireless communication terminal 400 transmits data to thesecond wireless communication terminal 500. Specifically, the firstwireless communication terminal 400 may transmit data based on the frameindicating ready to receive data from the second wireless communicationterminal 500. At this time, the first wireless communication terminal400 may transmit information indicating that the data transmission iscompleted to the second wireless communication terminal 500. In such acase, the second wireless communication terminal 500 may enter a sleepmode based on the information indicating that the data transmission iscompleted. Specifically, the second wireless communication terminal 500may maintain the sleep mode until data transmission for another secondwireless communication terminal 500 included in the same RF-chain iscompleted. In a specific embodiment, the second wireless communicationterminal 500 may maintain the sleep mode for a time obtained bysubtracting the elapsed time from the duration field value of the frameindicating the channel allocated to the second wireless communicationterminal 500 or the duration field value of the CTS-to-Self frame. Theinformation indicating that the transmission is terminated may bepredefined. Additionally, the information indicating that thetransmission is terminated may have a repeated specific pattern.Specifically, the information indicating that the transmission isterminated may be similar to the auto-detection pattern of the preambleof 802.11ac. In a specific embodiment, the information indicating thatthe transmission is terminated may be referred to as an ending-tone asdescribed above.

In another specific embodiment, without the information indicating thatthe transmission is terminated, the second wireless communicationterminal 500 may enter the sleep mode after a value of the durationfield of a frame indicating a channel allocated to the second wirelesscommunication terminal 500. In such a case, the duration field value ofthe frame indicating the channel allocated to the second wirelesscommunication terminal 500 indicates the time required for transmittingdata to be transmitted to the second wireless communication terminal500.

In another specific embodiment, the second wireless communicationterminal 500 may perform the sleep mode based on information indicatingthe number of symbols of data included in the preamble of a signalincluding data. Specifically, the second wireless communication terminal500 may receive data as many as the number of symbols indicated by theinformation indicating the number of symbols of data and then, enter thesleep mode. At this time, the preambles of all signals transmitted by asub-channel unit may include information indicating the number ofsymbols of data. At this time, the information indicating the number ofsymbols of data included in the preamble of the signal may be referredto as a length field.

When data transmission to all of the plurality of second wirelesscommunication terminals 500 is completed, the second wirelesscommunication terminal 500 entering the sleep mode may wake-up. At thistime, the second wireless communication terminal 500 may wake-up whenall the data transmissions for the plurality of second wirelesscommunication terminals 500 are completed.

In addition, the first wireless communication terminal 400 may transmitdata to another second wireless communication terminal 500 whose datatransmission is not completed through a channel allocated to any onesecond wireless communication terminal 500 whose data transmission iscompleted. Specifically, another second wireless communication terminal500 may be a second wireless communication terminal 500 whose datatransmission is not completed among a plurality of second wirelesscommunication terminals 500. In another specific embodiment, anothersecond wireless communication terminal 500 may be a second wirelesscommunication terminal 500 that does not start to receive data when thedata transmission for any one second wireless communication terminal 500is completed.

In addition, as described above, while transmitting data to theplurality of second wireless communication terminals 500, the firstwireless communication terminal 400 may transmit information indicatingthat the data transmission is completed to a second wirelesscommunication terminal 500 whose data transmission is completed firstamong the plurality of second wireless communication terminals 500.After transmitting the information indicating that the data transmissionis completed, the first wireless communication terminal 400 may transmitdata to another second wireless communication terminal 500 through achannel allocated to a second wireless communication terminal 500 whosedata transmission is completed first among the plurality of secondwireless communication terminals 500.

At this time, the first wireless communication terminal 400 may transmita guard interval signal after transmitting information indicating thatthe data transmission is completed in order to prevent interferencebetween signals. After transmitting the guard interval signal, the firstwireless communication terminal 400 may transmit data to another secondwireless communication terminal 500 through a channel allocated to asecond wireless communication terminal 500 whose data transmission iscompleted first among the plurality of second wireless communicationterminals 500. At this time, the guard interval signal may be a Nullingsignal.

The plurality of second wireless communication terminals 500 thatreceive data may transmit the frame indicating whether data is receivedto the first wireless communication terminal 400.

In another specific embodiment, the second wireless communicationterminal 500 that first complete data reception among the plurality ofsecond wireless communication terminals 500 may transmit to anothersecond wireless communication terminal 500 a frame indicating whetherthe second wireless communication terminal 500 receives the data.Specifically, the second wireless communication terminal 500 thatreceives the information indicating that the transmission is terminatedmay transmit to another second wireless communication terminal 500 aframe indicating whether the second wireless communication terminal 500receives data. For example, the second wireless communication terminal500 may transmit a frame indicating whether data is received to anothersecond wireless communication terminal 500 through a channel allocatedto the second wireless communication terminal 500. At this time, anothersecond wireless communication terminal 500 may be a second wirelesscommunication terminal that currently receives data. In addition, aframe indicating whether data is received or not may be referred to asan sACK as described above.

After the completion of all the data transmission for the plurality ofsecond wireless communication terminals 500, another second wirelesscommunication terminal 500 that receives the frame indicating whetherdata is received may transmit a frame indicating that the plurality ofsecond wireless communication terminals 500 receive data. Specifically,another second wireless communication terminal 500 that receives theframe indicating whether data is received may transmit a frameindicating whether the plurality of second wireless communicationterminals 500 receive data through a channel including a sub-channelallocated to the second wireless communication terminal 500. At thistime, the frame indicating whether the plurality of second wirelesscommunication terminals 500 receive data may be referred to as an AggACK. A specific method of generating the Agg ACK may be based on theembodiment described with reference to FIGS. 13 to 15.

In another specific embodiment, the second wireless communicationterminal may receive data and transmit a Block ACK frame as a frameindicating whether data is received. At this time, the block ACK frameis a frame indicating whether a plurality of data frames are received.The plurality of second wireless communication terminals 500, whichrespectively receive a plurality of sub-channels of the same channel,may sequentially transmit block ACK frames to the access point APthrough a corresponding channel. At this point, the order oftransmitting a block ACK frame from the second wireless communicationterminal 500 to the first wireless communication terminal 400 may be anarrangement order of information on a channel allocated to the secondwireless communication terminal 500 included in the frame indicating achannel allocated to the second wireless communication terminal 500.

FIG. 24 is a ladder diagram illustrating a frame transmission operationof a wireless communication terminal according to an embodiment of thepresent invention.

As described above, when one RF-chain is used in the communicationbetween the first wireless communication terminal and the plurality ofsecond wireless communication terminals, the first wirelesscommunication terminal may independently perform switching betweentransmission and reception for each of the plurality of second wirelesscommunication terminals. Therefore, the first wireless communicationterminal needs to synchronize switching between transmission andreception for each of the plurality of second wireless communicationterminals. In addition, the first wireless communication terminal thatcommunicates with the plurality of second wireless communicationterminals has a larger computation burden than the first wirelesscommunication terminal that communicates with one second wirelesscommunication terminal. In order to solve such a problem, the firstwireless communication terminal or the second wireless communicationterminal may repeatedly transmit dummy data or the same frame.Specifically, the wireless communication terminal may perform thefollowing operations.

The wireless communication terminal transmits a frame to anotherwireless communication terminal (S2401). At this time, the wirelesscommunication terminal that transmits the frame may be the firstwireless communication terminal, and the wireless communication terminalthat receives the frame may be the second wireless communicationterminal. In another specific embodiment, the wireless communicationterminal that transmits the frame may be the second wirelesscommunication terminal, and the wireless communication terminal thatreceives the frame may be the first wireless communication terminal.

In addition, the frame transmitted by the wireless communicationterminal may be a data frame including data. In another specificembodiment, the frame transmitted by the wireless communication terminalmay be a control frame.

The wireless communication terminal transmits dummy data to anotherwireless communication terminal or transmits the same frame repeatedly(S2403). Specifically, the wireless communication terminal may transmita data frame to another wireless communication terminal, transmit dummydata, or repeatedly transmit the same frame. In a specific embodiment,the wireless communication terminal may transmit the FCS field of thedata frame to another wireless communication terminal, and then transmitdummy data or repeatedly transmit the same frame. At this time, thedummy data may indicate meaningless data that is distinguished frommeaningful data transmitted through a data frame. Specifically, thedummy data may be a continuous pattern of a specific value such as “0”.

Through this operation, the wireless communication terminal may preventanother wireless communication terminal from accessing a channel beforeswitching between transmission and reception of the RF-chain. Inaddition, through this, the wireless communication terminal may reducethe processing burden of a terminal that receives a frame.

As described above, although wireless LAN communication is exemplarilydescribed for the present invention, the present invention is notlimited thereto and may be identically applied to another communicationsystem such as cellular communication. In addition, although the method,device and system of the present invention are described in relation tospecific embodiments, the configuration elements, a part of or theentirety of operations of the present invention may be implemented usinga computer system having general purpose hardware architecture.

In the foregoing, features, structures, or effects described inconnection with embodiments are included in at least one embodiment, andare not necessarily limited to one embodiment. Furthermore, theexemplified features, structures, or effects in various embodiments canbe combined and modified by those skilled in the art. Accordingly,contents in connection with these combination and modification should beconstrued to fall in the scope of the present invention.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthe present invention. For example, variations and modifications in thecomponent parts and/or arrangements, alternative uses will also beapparent to those skilled in the art. In addition, differences relatedto such modifications and application should be interpreted to be withinthe scope of the present invention defined in the appended claims.

The invention claimed is:
 1. A wireless communication terminalcomprising: a transceiver; and a processor, wherein the processor isconfigured to: receive, by using the transceiver, data from a basewireless communication terminal through a sub-band while the basewireless communication terminal is performing simultaneous transmissionto the wireless communication terminal and one or more other wirelesscommunication terminals other than the wireless communication terminalthrough one or more other sub-bands, wherein the simultaneoustransmission is transmitted through a frequency band including thesub-band and other sub-bands by using orthogonal frequency divisionmultiplexing access (OFDMA), when a transmission of data to the wirelesscommunication terminal from the base wireless communication terminalduring the simultaneous transmission is terminated, enter a sleep modefor power saving while a transmission of data to the one or more otherwireless communication terminals from the base wireless communicationterminal during the simultaneous transmission is going on, wherein adummy data including value 0 is transmitted from the base wirelesscommunication terminal after the transmission of the data to thewireless communication terminal is terminated during the simultaneoustransmission, and the dummy data is transmitted until the transmissionof the data to the one or more other wireless communication terminals isterminated, and wake up from the sleep mode based on an end of thesimultaneous transmission.
 2. The wireless communication terminal ofclaim 1, wherein the transceiver is configured to receive informationindicating that the transmission of the data to the wirelesscommunication terminal during the simultaneous transmission isterminated, wherein the processor is configured to enter the sleep modebased on the information.
 3. An operation method of a wirelesscommunication terminal, the method comprising: receiving data from thebase wireless communication terminal through a sub-band, while the basewireless communication terminal is performing simultaneous transmissionto the wireless communication terminal and one or more other wirelesscommunication terminals other than the wireless communication terminalthrough one or more other sub-bands, wherein the simultaneoustransmission is transmitted through a frequency band including thesub-band and other sub-bands by using orthogonal frequency divisionmultiplexing access (OFDMA); when a transmission of data to the wirelesscommunication terminal during the simultaneous transmission isterminated, entering a sleep mode for power saving while a transmissionof data to the one or more other wireless communication terminals fromthe base wireless communication terminal during the simultaneoustransmission is going on, wherein a dummy data including value 0 istransmitted from the base wireless communication terminal after thetransmission of the data to the wireless communication terminal isterminated during the simultaneous transmission, and the dummy data istransmitted until the transmission of the data to the one or more otherwireless communication terminals is terminated; and waking up from thesleep mode based on an end of the simultaneous transmission.
 4. Themethod of claim 3, wherein the entering a sleep mode comprises:receiving information indicating that the transmission of the data tothe wireless communication terminal during the simultaneous transmissionis terminated, and entering the sleep mode based on the information.